Pavement Performance Measures and Forecasting and The Effects of Maintenance and Rehabilitation Strategy on Treatment Effectiveness (Revised)

CHAPTER 6. LTPP DATA ANALYSES OF RIGID PAVEMENTS

Chapter 5 presented the results of the analyses of the time-series condition and distress data of the LTPP flexible pavement test sections. This chapter presents the results of the analyses of the time-series condition and distress data of the LTPP rigid pavement test sections. Once again, the data used in this study were obtained from the LTPP database Standard Data Release 28.0.

IMPACTS OF MAINTENANCE TREATMENTS ON PAVEMENT CONDITION AND DISTRESS USING THE LTPP SPS-2 TEST SECTIONS

The main objective of the SPS-2 experiment was to study the effects of the following:⁽⁷⁵⁾

• Climatic region.
  
  
• Drainage.
  
  
• Slab thickness (8 and 11 inches (203 and 279 mm)).
  
  
• The 14-day concrete flexural strength (551 and 899 lbf/inch² (3.8 and 6.2 MPa)).
  
  
• Slab width (12 and 14 ft (3.66 and 4.27 m)).
  
  
• Base type (dense-graded aggregate base, asphalt-treated base, permeable asphalt-treated base, and a combination thereof).

Analysis Steps

In this study, the analyses of the impacts of the various design variables were accomplished using the following steps:

• Step 1: For each pavement test section in the LTPP SPS-2 experiment, the time-dependent pavement condition (IRI) and distress (transverse and longitudinal cracking) data were downloaded from the LTPP database, organized, and analyzed. Results of the analyses included the RFP and RSP of each test section calculated as the time period from the time of construction to the time when the pavement condition or distress reached the appropriate threshold values. The reason for calculating RFP and RSP from the construction data (surface age is 0 years) was that the dates of construction and the dates of the last data collection for the SPS-2 test sections were not the same. The implication of this is that the reference time for each SPS-2 test section was taken as the date of construction.
  
  
• Step 2: For each pavement condition and distress type, the resulting RFPs and RSPs and other inventory data (such as SHRP ID, State, slab thickness, drainage, slab width, concrete flexural strength, and so forth) were then organized in a Microsoft® Excel spreadsheet format.
  
  
• Step 3: For each SHRP ID and for each pavement condition and distress type, the minimum and maximum RFPs and RSPs and their averages were calculated and listed in the Microsoft® Excel spreadsheets.
  
  
• Step 4: The data were then organized into the following groups and subgroups and in table 77. The main objective of the division was to separate the design variables affecting pavement performance.
  
  
  • Climatic region groups: The results of the analyses were organized into the four climatic regions—WF, WNF, DF, and DNF.
    
    
  • Slab thickness subgroups: The results of the analyses in each climatic region were then organized into two subgroups based on the slab thicknesses of 8 and 11 inches (203 and 279 mm).
    
    
  • Slab width subgroups: The results of the analyses in each slab thickness subgroup were then organized into two subgroups based on the slab widths of 12 and 14 ft (3.66 and 4.27 m).
    
    
  • Concrete flexural strength subgroups: The results in each slab width subgroup were then organized into two subgroups based on the concrete 14day flexural strength of 551 and 899 lbf/inch² (3.8 and 6.2 MPa).
    
    
  • Drainage subgroups: The results in each concrete flexural strength subgroup were further divided into two drainage subgroups (presence and absence of drainage).

Table 77. Analysis subgroups and the number of test sections available for analyses in the LTPP SPS-2 experiment in each subgroup.

Condition/ Distress Type	Lane Width (ft)	Slab Strength (lbf/inches2)	Slab Thickness (inches)	Number of Available Test Sections Based on Climatic Region and Presence of Aggregate Base Drainage
				WF		WNF		DF		DNF
				D	ND	D	ND	D	ND	D	ND
IRI	12	500	8	1	4	1	4	2	2	1	2
			11	3	8	1	2	3	2	1	2
		900	8	3	7	1	2	3	2	1	1
			11	1	3	2	3	1	2	1	2
	14	500	8	3	6	1	2	3	2	1	2
			11	1	4	1	4	1	2	1	2
		900	8	2	4	0	4	2	2	1	2
			11	2	7	0	2	2	2	1	2
Longitudinal cracking	12	500	8	2	3	1	4	2	3	1	2
			11	4	8	1	2	1	2	1	2
		900	8	4	8	1	2	0	2	1	2
			11	2	3	2	4	1	2	1	2
	14	500	8	4	7	1	2	1	2	1	2
			11	2	4	2	4	2	2	1	2
		900	8	2	4	0	4	2	2	1	2
			11	4	7	0	2	1	2	1	2
Transverse tracking	12	500	8	2	3	1	4	2	2	1	2
			11	4	8	1	2	1	2	1	2
		900	8	4	8	1	2	0	2	1	2
			11	2	3	2	4	1	2	1	2
	14	500	8	4	7	1	2	1	2	1	2
			11	2	4	2	4	2	2	1	2
		900	8	2	4	0	4	2	2	1	2
			11	4	7	0	2	1	2	1	1
1 ft = 0.305 m. 1 lbf/inch2 = .00690 MPa. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Analyses Results

The detailed analysis results were submitted to FHWA and are available from the LTPP Customer Support Services.⁽⁷⁹⁾ For convenience, the detailed results are summarized in table 78 through table 89. Because there are many design variables, four tables were populated to summarize the impacts of the design variables on RFP or RSP for each pavement condition or distress. Each table summarizes the impacts of the climatic region, slab thickness, drainable bases, and a combination of slab width and concrete flexural strength on the RFP or RSP of test sections based on one condition (IRI) or one distress (longitudinal or transverse cracks). For example, table 78 summarizes the results of the analyses of the impacts of design factors on RFP based on the IRI of SPS-2 test sections having slab width 12 ft (3.66 m) and concrete flexural strength 551 lbf/inch² (3.8 MPa), while table 79 summarizes the results of analyses of the impacts of design factors on RFP based on the IRI of SPS-2 test sections having slab width 14 ft (4.27m) and concrete flexural strength 551 lbf/inch² (3.8 MPa). The numbers in the tables indicate the differences in years in RFPs or RSPs of the SPS-2 test sections having the top heading parameters relative to RFPs and RSPs of the SPS-2 test sections having the side heading parameters. The explanation of the listed numbers in the tables is the same as that included in chapter 5 in table 29 through table 33. For convenience, the following paragraphs explain the listed numbers in table 78 through table 89 using the data from the first and second rows in table 78.

Table 78. Summary of the results of the analyses of the impacts of design factors on RFP based on IRI of LTPP SPS-2 test sections with slab width of 12 ft (3.66 m) and concrete flexural strength of 551 lbf/inch² (3.8 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	0	0	–2	0	0	0	0	0	0	0	0	0	–3	0	0
		ND	0	*	0	–1	0	0	0	0	0	0	0	0	0	–3	0	0
	11	D	0	0	*	–2	0	0	0	0	0	0	0	0	0	–3	0	0
		ND	2	1	2	*	2	2	2	2	2	2	2	2	2	–2	2	2
WNF	8	D	0	0	0	–2	*	0	0	0	0	0	0	0	0	–3	0	0
		ND	0	0	0	–2	0	*	0	0	0	0	0	0	0	–3	0	0
	11	D	0	0	0	–2	0	0	*	0	0	0	0	0	0	–3	0	0
		ND	0	0	0	–2	0	0	0	*	0	0	0	0	0	–3	0	0
DF	8	D	0	0	0	–2	0	0	0	0	*	0	0	0	0	–3	0	0
		ND	0	0	0	2	0	0	0	0	0	*	0	0	0	–3	0	0
	11	D	0	0	0	–2	0	0	0	0	0	0	*	0	0	–3	0	0
		ND	0	0	0	–2	0	0	0	0	0	0	0	*	0	–3	0	0
DNF	8	D	0	0	0	–2	0	0	0	0	0	0	0	0	*	–3	0	0
		ND	3	3	3	2	3	3	3	3	3	3	3	3	3	*	3	3
	11	D	0	0	0	–2	0	0	0	0	0	0	0	0	0	–3	*	0
		ND	0	0	0	–2	0	0	0	0	0	0	0	0	0	–3	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Table 79. Summary of the results of analyses of the impacts of design factors on RFP based on IRI of LTPP SPS-2 test sections with slab width 14 ft (4.27 m) and concrete flexural strength of 551 lbf/inch² (3.8 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–4	0	0	0	–1	0	0	0	0	0	0	0	0	0	–2
		ND	4	*	4	4	4	3	4	4	4	4	4	4	4	4	4	2
	11	D	0	–4	*	0	0	–1	0	0	0	0	0	0	0	0	0	–2
		ND	0	–4	0	*	0	–1	0	0	0	0	0	0	0	0	0	–2
WNF	8	D	0	–4	0	0	*	–1	0	0	0	0	0	0	0	0	0	–2
		ND	1	–3	1	1	1	*	1	1	1	1	1	1	1	1	1	–1
	11	D	0	–4	0	0	0	–1	*	0	0	0	0	0	0	0	0	–2
		ND	0	–4	0	0	0	–1	0	*	0	0	0	0	0	0	0	–2
DF	8	D	0	–4	0	0	0	–1	0	0	*	0	0	0	0	0	0	–2
		ND	0	–4	0	0	0	–1	0	0	0	*	0	0	0	0	0	–2
	11	D	0	–4	0	0	0	–1	0	0	0	0	*	0	0	0	0	–2
		ND	0	–4	0	2	0	–1	0	0	0	0	0	*	0	0	0	–2
DNF	8	D	0	–4	0	0	0	–1	0	0	0	0	0	0	*	0	0	–2
		ND	0	–4	0	0	0	–1	0	0	0	0	0	0	0	*	0	–2
	11	D	0	–4	0	0	0	–1	0	0	0	0	0	0	0	0	*	–2
		ND	2	–2	2	2	2	1	2	2	2	2	2	2	2	2	2	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Table 80. Summary of the results of analyses of the impacts of design factors on RFP based on IRI of LTPP SPS-2 test sections with slab width 12 ft (3.66 m) and concrete flexural strength of 899 lbf/inch² (6.2 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–4	0	0	0	–2	0	0	NC	0	NC	0	0	0	0	0
		ND	4	*	4	4	4	2	4	4	NC	4	NC	4	4	4	4	4
	11	D	0	–4	*	0	0	–2	0	0	NC	0	NC	0	0	0	0	0
		ND	0	–4	0	*	0	–2	0	0	NC	0	NC	0	0	0	0	0
WNF	8	D	0	–4	0	0	*	–2	0	0	NC	0	NC	0	0	0	0	0
		ND	2	–2	2	2	2	*	2	2	NC	2	NC	2	2	2	2	2
	11	D	0	–4	0	0	0	–2	*	0	NC	0	NC	0	0	0	0	0
		ND	0	–4	0	0	0	–2	0	*	NC	0	NC	0	0	0	0	0
DF	8	D	NC	NC	NC	0	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC
		ND	0	–4	0	0	0	–2	0	0	NC	*	NC	0	0	0	0	0
	11	D	NC	NC	NC	0	NC	NC	NC	NC	NC	NC	*	NC	NC	NC	NC	NC
		ND	0	–4	0	0	0	–2	0	0	NC	0	NC	*	0	0	0	0
DNF	8	D	0	–4	0	0	0	–2	0	0	NC	0	NC	0	*	0	0	0
		ND	0	–4	0	0	0	–2	0	0	NC	0	NC	0	0	*	0	0
	11	D	0	–4	0	0	0	–2	0	0	NC	0	NC	0	0	0	*	0
		ND	0	–4	0	0	0	–2	0	0	NC	0	NC	0	0	0	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base. NC = Could not be compared.

 

Table 81. Summary of the results of analyses of the impacts of design factors on RFP based on IRI of LTPP SPS-2 test sections with slab width 14 ft (4.27 m) and concrete flexural strength of 899 lbf/inch² (6.2 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	0	0	0	NC	0	NC	0	0	0	NC	0	0	0	0	0
		ND	0	*	0	0	NC	0	NC	0	0	0	NC	0	0	0	0	0
	11	D	0	0	*	0	NC	0	NC	0	0	0	NC	0	0	0	0	0
		ND	0	0	0	*	NC	0	NC	0	0	0	NC	0	0	0	0	0
WNF	8	D	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC	NC	NC	NC	NC
		ND	0	0	0	0	NC	*	NC	0	0	0	NC	0	0	0	0	0
	11	D	NC	NC	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC	NC	NC
		ND	0	0	0	0	NC	0	NC	*	0	0	NC	0	0	0	0	0
DF	8	D	0	0	0	0	NC	0	NC	0	*	0	NC	0	0	0	0	0
		ND	0	0	0	0	NC	0	NC	0	0	*	NC	0	0	0	0	0
	11	D	NC	NC	NC	0	NC	NC	NC	NC	NC	NC	*	NC	NC	NC	NC	NC
		ND	0	0	0	0	NC	0	NC	0	0	0	NC	*	0	0	0	0
DNF	8	D	0	0	0	0	NC	0	NC	0	0	0	NC	0	*	0	0	0
		ND	0	0	0	0	NC	0	NC	0	0	0	NC	0	0	*	0	0
	11	D	0	0	0	0	NC	0	NC	0	0	0	NC	0	0	0	*	0
		ND	0	0	0	0	NC	0	NC	0	0	0	NC	0	0	0	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base. NC = Could not be compared.

 

Table 82. Summary of the results of analyses of the impacts of design factors on RSP based on longitudinal cracking of LTPP SPS-2 test sections with slab width 12 ft (3.66m) and concrete flexural strength of 551 lbf/inch² (3.8 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–2	0	0	0	–1	0	0	0	–3	0	0	0	–7	0	0
		ND	2	*	2	2	2	1	2	2	2	–1	2	2	2	–5	2	2
	11	D	0	–2	*	0	0	–1	0	0	0	–3	0	0	0	–7	0	0
		ND	0	–2	0	*	0	–1	0	0	0	–3	0	0	0	–7	0	0
WNF	8	D	0	–2	0	0	*	–1	0	0	0	–3	0	0	0	–7	0	0
		ND	1	–1	1	1	1	*	1	1	0	–2	1	1	1	–6	1	1
	11	D	0	–2	0	0	0	–1	*	0	0	–3	0	0	0	–7	0	0
		ND	0	–2	0	0	0	–1	0	*	0	–3	0	0	0	–7	0	0
DF	8	D	0	–2	0	0	0	0	0	0	*	–3	0	0	0	–6	0	0
		ND	3	1	3	7	3	2	3	3	3	*	3	3	3	–4	3	3
	11	D	0	–2	0	0	0	–1	0	0	0	–3	*	0	0	–7	0	0
		ND	0	–2	0	0	0	–1	0	0	0	–3	0	*	0	–7	0	0
DNF	8	D	0	–2	0	0	0	–1	0	0	0	–3	0	0	*	–7	0	0
		ND	7	5	7	7	7	6	7	7	6	4	7	7	7	*	7	7
	11	D	0	–2	0	0	0	–1	0	0	0	–3	0	0	0	–7	*	0
		ND	0	–2	0	0	0	–1	0	0	0	–3	0	0	0	–7	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Table 83. Summary of the results of analyses of the impacts of design factors on RSP based on longitudinal cracking of LTPP SPS-2 test sections with slab width 14ft (4.27m) and concrete flexural strength of 551 lbf/inch² (3.8 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–3	0	0	0	–7	0	0	0	0	0	–3	0	0	0	0
		ND	3	*	3	3	3	–4	3	3	3	3	3	1	3	3	3	3
	11	D	0	–3	*	0	0	–7	0	0	0	0	0	–3	0	0	0	0
		ND	0	–3	0	*	0	–7	0	0	0	0	0	–3	0	0	0	0
WNF	8	D	0	–3	0	0	*	–7	0	0	0	0	0	–3	0	0	0	0
		ND	7	4	7	7	7	*	7	7	7	7	7	5	7	7	7	7
	11	D	0	–3	0	0	0	–7	*	0	0	0	0	–3	0	0	0	0
		ND	0	–3	0	0	0	–7	0	*	0	0	0	–3	0	0	0	0
DF	8	D	0	–3	0	0	0	–7	0	0	*	0	0	–3	0	0	0	0
		ND	0	–3	0	0	0	–7	0	0	0	*	0	–3	0	0	0	0
	11	D	0	–3	0	0	0	–7	0	0	0	0	*	–3	0	0	0	0
		ND	3	–1	3	0	3	–5	3	3	3	3	3	*	3	3	3	3
DNF	8	D	0	–3	0	0	0	–7	0	0	0	0	0	–3	*	0	0	0
		ND	0	–3	0	0	0	–7	0	0	0	0	0	–3	0	*	0	0
	11	D	0	–3	0	0	0	–7	0	0	0	0	0	–3	0	0	*	0
		ND	0	–3	0	0	0	–7	0	0	0	0	0	–3	0	0	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Table 84. Summary of the results of analyses of the impacts of design factors on RSP based on longitudinal cracking of LTPP SPS-2 test sections with slab width 12 ft (3.66m) and concrete flexural strength of 899 lbf/inch² (6.2 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–2	0	–2	0	–3	0	0	NC	0	0	0	0	0	0	0
		ND	2	*	2	–1	2	–1	2	2	NC	2	2	2	2	2	2	2
	11	D	0	–2	*	–2	0	–3	0	0	NC	0	0	0	0	0	0	0
		ND	2	1	2	*	2	–1	2	2	NC	2	2	2	2	2	2	2
WNF	8	D	0	–2	0	–2	*	–3	0	0	NC	0	0	0	0	0	0	0
		ND	3	1	3	1	3	*	3	3	NC	3	3	3	3	3	3	3
	11	D	0	–2	0	–2	0	–3	*	0	NC	0	0	0	0	0	0	0
		ND	0	–2	0	–2	0	–3	0	*	NC	0	0	0	0	0	0	0
DF	8	D	NC	NC	NC	–2	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC
		ND	0	–2	0	–2	0	–3	0	0	NC	*	0	0	0	0	0	0
	11	D	0	–2	0	–2	0	–3	0	0	NC	0	*	0	0	0	0	0
		ND	0	–2	0	–2	0	–3	0	0	NC	0	0	*	0	0	0	0
DNF	8	D	0	–2	0	–2	0	–3	0	0	NC	0	0	0	*	0	0	0
		ND	0	–2	0	–2	0	–3	0	0	NC	0	0	0	0	*	0	0
	11	D	0	–2	0	–2	0	–3	0	0	NC	0	0	0	0	0	*	0
		ND	0	–2	0	–2	0	–3	0	0	NC	0	0	0	0	0	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base. NC = Could not be compared.

 

Table 85. Summary of the results of analyses of the impacts of design factors on RSP based on longitudinal cracking of LTPP SPS-2 test sections with slab width 14 ft (4.27m) and concrete flexural strength of 899 lbf/inch² (6.2 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	0	0	0	NC	0	NC	0	–1	0	0	–3	0	0	0	0
		ND	0	*	0	0	NC	0	NC	0	–1	0	0	–3	0	0	0	0
	11	D	0	0	*	0	NC	0	NC	0	–1	0	0	–3	0	0	0	0
		ND	0	0	0	*	NC	0	NC	0	–1	0	0	–3	0	0	0	0
WNF	8	D	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC	NC	NC	NC	NC
		ND	0	0	0	0	NC	*	NC	0	–1	0	0	–3	0	0	0	0
	11	D	NC	NC	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC	NC	NC
		ND	0	0	0	0	NC	0	NC	*	–1	0	0	–3	0	0	0	0
DF	8	D	1	1	1	0	NC	1	NC	1	*	1	1	–2	1	1	1	1
		ND	0	0	0	0	NC	0	NC	0	–1	*	0	–3	0	0	0	0
	11	D	0	0	0	0	NC	0	NC	0	–1	0	*	–3	0	0	0	0
		ND	3	3	3	0	NC	3	NC	3	2	3	3	*	3	3	3	3
DNF	8	D	0	0	0	0	NC	0	NC	0	–1	0	0	–3	*	0	0	0
		ND	0	0	0	0	NC	0	NC	0	–1	0	0	–3	0	*	0	0
	11	D	0	0	0	0	NC	0	NC	0	–1	0	0	–3	0	0	*	0
		ND	0	0	0	0	NC	0	NC	0	–1	0	0	–3	0	0	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base. NC = Could not be compared.

 

Table 86. Summary of the results of analyses of the impacts of design factors on RSP based on transverse cracking of LTPP SPS-2 test sections with slab width 12 ft (3.66m) and concrete flexural strength of 551 lbf/inch² (3.8 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–6	1	–1	1	–4	1	1	1	1	1	1	1	–12	1	1
		ND	6	*	6	5	6	2	6	6	6	6	6	6	6	–6	6	6
	11	D	–1	–6	*	–2	0	–4	0	0	0	0	0	0	0	–12	0	0
		ND	1	–5	2	*	2	–3	2	2	2	2	2	2	2	–11	2	2
WNF	8	D	–1	–6	0	–2	*	–4	0	0	0	0	0	0	0	–12	0	0
		ND	4	–2	4	3	4	*	4	4	4	4	4	4	4	–8	4	4
	11	D	–1	–6	0	–2	0	–4	*	0	0	0	0	0	0	–12	0	0
		ND	–1	–6	0	–2	0	–4	0	*	0	0	0	0	0	–12	0	0
DF	8	D	–1	–6	0	–2	0	–4	0	0	*	0	0	0	0	–12	0	0
		ND	–1	–6	0	11	0	–4	0	0	0	*	0	0	0	–12	0	0
	11	D	–1	–6	0	–2	0	–4	0	0	0	0	*	0	0	–12	0	0
		ND	–1	–6	0	–2	0	–4	0	0	0	0	0	*	0	–12	0	0
DNF	8	D	–1	–6	0	–2	0	–4	0	0	0	0	0	0	*	–12	0	0
		ND	12	6	12	11	12	8	12	12	12	12	12	12	12	*	12	12
	11	D	–1	–6	0	–2	0	–4	0	0	0	0	0	0	0	–12	*	0
		ND	–1	–6	0	–2	0	–4	0	0	0	0	0	0	0	–12	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Table 87. Summary of the results of analyses of the impacts of design factors on RSP based on transverse cracking of LTPP SPS-2 test sections with slab width 14 ft (4.27m) and concrete flexural strength of 551 lbf/inch² (3.8 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–2	0	0	0	–5	0	0	0	0	0	0	0	–1	0	–1
		ND	2	*	2	2	2	–3	2	2	2	2	2	2	2	0	2	0
	11	D	0	–2	*	0	0	–5	0	0	0	0	0	0	0	–1	0	–1
		ND	0	–2	0	*	0	–5	0	0	0	0	0	0	0	–1	0	–1
WNF	8	D	0	–2	0	0	*	–5	0	0	0	0	0	0	0	–1	0	–1
		ND	5	3	5	5	5	*	5	5	5	5	5	5	5	3	5	3
	11	D	0	–2	0	0	0	–5	*	0	0	0	0	0	0	–1	0	–1
		ND	0	–2	0	0	0	–5	0	*	0	0	0	0	0	–1	0	–1
DF	8	D	0	–2	0	0	0	–5	0	0	*	0	0	0	0	–1	0	–1
		ND	0	–2	0	1	0	–5	0	0	0	*	0	0	0	–1	0	–1
	11	D	0	–2	0	0	0	–5	0	0	0	0	*	0	0	–1	0	–1
		ND	0	–2	0	1	0	–5	0	0	0	0	0	*	0	–1	0	–1
DNF	8	D	0	–2	0	0	0	–5	0	0	0	0	0	0	*	–1	0	–1
		ND	1	0	1	1	1	–3	1	1	1	1	1	1	1	*	1	0
	11	D	0	–2	0	0	0	–5	0	0	0	0	0	0	0	–1	*	–1
		ND	1	0	1	1	1	–3	1	1	1	1	1	1	1	0	1	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base.

 

Table 88. Summary of the results of analyses of the impacts of design factors on RSP based on transverse cracking of LTPP SPS-2 test sections with slab width 12 ft (3.66m) and concrete flexural strength of 899 lbf/inch² (6.2 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	–1	–2	–5	1	–5	1	1	NC	1	1	1	1	1	1	1
		ND	1	*	0	–3	2	–4	2	2	NC	2	2	2	2	2	2	2
	11	D	2	0	*	–3	3	–4	3	3	NC	3	3	3	3	3	3	3
		ND	5	3	3	*	6	–1	6	6	NC	6	6	6	6	6	6	6
WNF	8	D	–1	–2	–3	–6	*	–6	0	0	NC	0	0	0	0	0	0	0
		ND	5	4	4	1	6	*	6	6	NC	6	6	6	6	6	6	6
	11	D	–1	–2	–3	–6	0	–6	*	0	NC	0	0	0	0	0	0	0
		ND	–1	–2	–3	–6	0	–6	0	*	NC	0	0	0	0	0	0	0
DF	8	D	NC	NC	NC	–6	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC
		ND	–1	–2	–3	–6	0	–6	0	0	NC	*	0	0	0	0	0	0
	11	D	–1	–2	–3	–6	0	–6	0	0	NC	0	*	0	0	0	0	0
		ND	–1	–2	–3	–6	0	–6	0	0	NC	0	0	*	0	0	0	0
DNF	8	D	–1	–2	–3	–6	0	–6	0	0	NC	0	0	0	*	0	0	0
		ND	–1	–2	–3	–6	0	–6	0	0	NC	0	0	0	0	*	0	0
	11	D	–1	–2	–3	–6	0	–6	0	0	NC	0	0	0	0	0	*	0
		ND	–1	–2	–3	–6	0	–6	0	0	NC	0	0	0	0	0	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base. NC = Could not be compared.

 

Table 89. Summary of the results of analyses of the impacts of design factors on RSP based on transverse cracking of LTPP SPS-2 test sections with slab width 14 ft (4.27m) and concrete flexural strength of 899 lbf/inch² (6.2 MPa).

Climatic Region	PCC Slab Thickness (inches)	Base Type	Differences Between RFP of the Top Heading and RFP of the Side Heading (Year)
			WF				WNF				DF				DNF
			8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC		8-inch PCC		11-inch PCC
			D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND	D	ND
WF	8	D	*	2	2	2	NC	2	NC	2	5	2	2	0	2	3	2	2
		ND	2	*	4	4	NC	4	NC	4	3	4	4	2	4	1	4	4
	11	D	–2	4	*	0	NC	0	NC	0	7	0	0	2	0	5	0	0
		ND	–2	4	0	*	NC	0	NC	0	7	0	0	2	0	5	0	0
WNF	8	D	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC	NC	NC	NC	NC
		ND	–2	4	0	0	NC	*	NC	0	7	0	0	2	0	5	0	0
	11	D	NC	NC	NC	NC	NC	NC	*	NC	NC	NC	NC	NC	NC	NC	NC	NC
		ND	–2	4	0	0	NC	0	NC	*	7	0	0	2	0	5	0	0
DF	8	D	5	3	7	0	NC	7	NC	7	*	7	7	5	7	2	7	7
		ND	–2	4	0	5	NC	0	NC	0	7	*	0	2	0	5	0	0
	11	D	–2	4	0	0	NC	0	NC	0	7	0	*	2	0	5	0	0
		ND	0	2	2	0	NC	2	NC	2	5	2	2	*	2	3	2	2
DNF	8	D	–2	4	0	0	NC	0	NC	0	7	0	0	2	*	5	0	0
		ND	3	1	5	5	NC	5	NC	5	2	5	5	3	5	*	5	5
	11	D	–2	4	0	0	NC	0	NC	0	7	0	0	2	0	5	*	0
		ND	–2	4	0	0	NC	0	NC	0	7	0	0	2	0	5	0	*
* Indicates the diagonal of the matrix where the top and the side headings are the same. 1 inch = 25.4 mm. D = Drainable base. ND = Undrainable base. NC = Could not be compared.

 

The following list describes the RFP of the SPS-2 test sections having 11-inch (279-mm)-thick slab and undrainable bases in the WF region:

• Two years less than the RFP of test sections located in the WF region and having 8-inch (203-mm)-thick slab and drainable bases.
  
  
• An insignificant 1 year less than the RFP of test sections located in the WF region and having 8-inch-thick slab and undrainable bases.

In the DNF region, the RFP of the SPS-2 test sections having 8-inch (203-mm)-thick slab and undrainable bases is 3 years less than the RFP of test sections located in the WF region and having 8-inch (203-mm)-thick slab and either drainable or undrainable bases.

It should be noted that the results listed in table 78 to table 89 are further summarized in table 90 based on the relative performance of comparable SPS-2 test sections. In this context, the term comparable implies SPS-2 test sections having the same slab thickness and slab width, the same concrete flexural strength, and similar bases. The summarized data in table 90 address the impact of the climatic regions on pavement performance in terms of functional condition (RFP based on IRI) and structural condition (RSP based on longitudinal and transverse cracking). The values in the table indicate the percent of the test sections, having the heading parameters that performed better, the same, or worse than the test sections having the side heading parameters. In the following sections, these values are presented and discussed for each pavement condition and distress type.

Table 90. Summary of the results of the analyses of the effects of climatic region on the performance of the LTPP SPS-2 test sections.

Condition/ Distress Type	Climatic Region	Percent of SPS-2 Test Sections Located in One Climatic Region That Performed Better, the Same, or Worse Than Compatible Test Sections Located in Other Regions
		WF			WNF			DF			DNF
		Better	Same	Worse	Better	Same	Worse	Better	Same	Worse	Better	Same	Worse
IRI	WF	—	—	—	26	70	4	32	68	0	26	65	9
	WNF	4	70	26	—	—	—	10	90	0	9	82	9
	DF	0	68	32	0	90	10	—	—	—	0	90	10
	DNF	9	65	26	9	82	9	10	90	0	—	—	—
Longitudinal Cracking	WF	—	—	—	13	78	9	14	68	18	17	79	4
	WNF	9	78	13	—	—	—	14	72	14	78	18	4
	DF	18	68	14	14	72	14	—	—	—	18	77	5
	DNF	4	79	17	4	18	78	5	77	18	—	—	—
Transverse Cracking	WF	—	—	—	39	44	17	48	43	9	39	35	26
	WNF	17	44	39	—	—	—	18	77	5	13	64	23
	DF	9	43	48	5	77	18	—	—	—	9	64	27
	DNF	26	35	39	23	64	13	27	64	9	—	—	—
— Indicates no data.

 

IRI

The data listed in the IRI rows in table 90 indicate that the pavement performance based on IRI, of the majority of the SPS-2 test sections, was not affected by the climatic regions. The various findings leading to this conclusion are detailed as follows:

• In the WF region, 70, 68, and 65 percent of the SPS-2 test sections performed the same as comparable test sections located in the WNF, DF, and DNF regions, respectively, while 26, 32, and 26 percent performed worse.
  
  
• In the WNF region, 90 and 82 percent of the SPS-2 test sections performed the same as comparable test sections located in the DF and DNF regions, respectively, while only 10and 9 percent performed worse.
  
  
• In the DF region, 90 percent of the SPS-2 test section performed the same as comparable test sections located in the DNF region, and only 10 percent performed better.

Longitudinal Cracking

The data listed in the longitudinal cracking rows in table 90 indicate the following:

• In the WF region, 78, 68, and 79 percent of the SPS-2 test sections performed the same as comparable test sections located in the WNF, DF, and DNF regions, respectively, while 13, 14, and 17 percent performed worse, and 9, 18, and 4 percent performed better. In the WNF region, 72 and 18 percent of the SPS-2 test sections performed the same as comparable test sections located in the DF and DNF regions, respectively, while 14 and 78 percent performed worse, and 14 and 4 percent performed better.
  
  
• In the DF region, 77 percent of the SPS-2 test section performed the same as comparable test sections located in the DNF region, and 18 percent performed worse.

Transverse Cracking

The data listed in the transverse cracking block of table 90 indicate the following:

• In the WF region, 44, 43, and 35 percent of the SPS-2 test sections performed the same as comparable test sections located in the WNF, DF, and DNF regions, respectively, while 17, 9, and 26 percent performed better, and 39, 48, and 39 percent performed worse.
  
  
• In the WNF region, the majority (77 and 64 percent) of the SPS-2 test sections performed the same as comparable test sections located in the DF and DNF regions, respectively, while few percentages performed either better or worse.
  
  
• Likewise, in the DF region, the majority of the SPS-2 test sections performed the same as comparable test sections located in the DNF region, while 27 percent performed better, and 9 percent performed worse.

Summary, Conclusions, and Recommendations for LTPP SPS-2

The available data in the LTPP database Standard Data Release 28.0 regarding the LTPP SPS-2 experiment were downloaded, organized, and analyzed. The intent was to study the impact of each design variable on pavement performance. When the data were divided into various groups based on separation of variables, the number of test sections under each variable was statistically insignificant. However, for each test section, the resulting RFPs and RSPs are listed in table 78 through table 89. Because of the limited number of SPS-2 test sections under each variable, the impact of the design variables on pavement performance was not analyzed or discussed any further. Rather, the data were summarized in table 90, and the impacts of the climatic region on pavement performance were presented after that table. Based on the analyses results, the following conclusions were drawn:

• On average, the pavement performance in terms of IRI was not affected by the climatic region, although the data indicated that SPS-2 test sections located in the WF region performed slightly worse than compatible test sections located in the other three climatic regions.
  
  
• On average, the majority of the SPS-2 test sections located in the WNF region performed worse in terms of longitudinal cracking than those in the DNF region. This was mainly due to the impact of excessive moisture on pavement performance.
  
  
• The WF region had a more damaging impact on pavement performance in terms of transverse cracking than on those in the WNF, DF, and DNF regions. This was expected, owing to the combined effects of subfreezing temperatures and moisture.

IMPACTS OF MAINTENANCE TREATMENTS ON PAVEMENT CONDITION AND DISTRESS USING THE LTPP SPS-4 TEST SECTIONS

The main objective of the LTPP SPS-4 experiment was to compare the performance of rigid pavement test sections subjected to selected maintenance treatments to the performance of untreated test sections or the control sections. The 34 SPS-4 test sites were initiated between 1990 and 1995 and are distributed across the United States and Canada. Each of the SPS-4 test sites consisted of three test sections. One each of two sections at each site was subjected to one or the other of the following two treatments:

• Joint and crack sealing (410).
  
  
• Joint undersealing (420).

(Note that the numbers in parentheses are the LTPP designation of the treatment. For example, the designation of the joint and crack sealing is 410.) The third section was counted as a control section that was not treated in accordance with the original experimental design. However, only 10 of the 34 test sites contained a test section that was joint undersealed, bringing the total number of test sections and control sections to 78.

Several variables affect the performance of the treated pavement sections. These include climatic region, traffic, subgrade type, etc. Similar to the SPS-3 experiment, unfortunately, in some scenarios, if these variables were separated, the number of test sections available for analyses became insignificant. To illustrate, table 91 lists the number of test sections available for analyses based on the separation of the following variables:

• Two treatment types.
  
  
• One pavement condition (IRI).
  
  
• Two pavement distress types (longitudinal and transverse cracking).
  
  
• Four climatic regions (WF, WNF, DF, and DNF).
  
  
• Three traffic levels.

Table 91. Number of test sections that have after treatment pavement condition and distress and traffic data.

Condition or Distress Type	Treatment Type	Number of Test Sections Subjected to Each of Three Traffic Levels in the Various Climatic Regions
		WF			WNF			DF			DNF
		L	M	H	L	M	H	L	M	H	L	M	H
IRI	Joint and crack sealing	0	0	7	1	3	6	0	0	2	0	0	2
	Joint undersealing	0	0	0	0	3	3	0	0	1	0	0	1
	Control section	0	0	7	1	3	7	0	0	1	0	0	2
Longitudinal cracking	Joint and crack sealing	0	0	0	0	2	3	0	0	0	0	0	0
	Joint undersealing	0	0	0	0	1	1	0	0	0	0	0	0
	Control section	0	0	1	0	2	0	0	0	1	0	0	2
Transverse cracking	Joint and crack sealing	0	0	1	0	1	3	0	0	1	0	0	0
	Joint undersealing	0	0	0	0	0	2	0	0	0	0	0	0
	Control section	0	0	2	0	1	2	0	0	1	0	0	1
Note: For each pavement condition and distress type, a test section was analyzed only if it exhibited any condition or distress and had three or more data points after treatment that could be modeled. L = Low traffic (0 to 60,000 ESAL/year). M = Medium traffic (61,000 to 120,000 ESAL/year). H = High traffic (> 120,000 ESAL/year).

 

It can be seen that for longitudinal and transverse cracking, the number of SPS-4 test sections that were available for analyses was statistically insignificant in all climatic regions. Therefore, the analyses were conducted to assess the impact of each treatment type in each climatic region and for each pavement condition and distress type. That is, the data were not separated based on traffic level or by the type of subbase or subgrade. Nevertheless, the analyses of the impacts of each of the two treatment types on pavement performance were accomplished using the following steps:

• Step 1: For each treated pavement test section in the SPS-4 experiment, each of the available pavement condition (IRI) and distress data were used to calculate the RFP and RSP of that section from the time of the treatment to the time when the pavement condition or distress reach the prespecified threshold values.
  
  
• Step 2: For each pavement condition and distress type and for each pavement treatment type, the minimum and maximum RFPs and RSPs and their averages for all test sections located in the same climatic region were calculated and are listed in table 92 through table 94 depending on the pavement condition and distress type.

Results of the analyses are discussed per pavement condition and distress type in the three subsections following table 92 through table 94.

Table 92. Impacts of various maintenance treatments and control section on pavement performance in terms of RFP based on IRI.

Climatic Region	Treatment Type	RFP (Year)								Difference in RFP (Year)
		Test Sections				Control Sections
		Number of Test Sections	Min	Max	Avg	Number of Test Sections	Min	Max	Avg
WF	Joint crack sealing	8	10	20	17	8	8	20	17	0
WNF		10	6	20	18	11	0	20	15	3
DF		4	1	16	9	2	11	13	12	3
DNF		2	5	20	12	2	17	17	17	4
WF	Joint undersealing	0	—	—	—	8	8	20	17	NC
WNF		6	0	20	12	11	0	20	15	3
DF		1	3	3	3	2	11	13	12	10
DNF		1	2	2	2	2	17	17	17	14
—Indicates no data. Min = Minimum. Max = Maximum. Avg = Average. NC = Could not be compared.

 

Table 93. Impacts of various maintenance treatments and control section on pavement performance in terms of RSP based on longitudinal cracking.

Climatic Region	Treatment Type	RFP (Year)								Difference in RSP (Year)
		Test Sections				Control Sections
		Number of Test Sections	Min	Max	Avg	Number of Test Sections	Min	Max	Avg
WF	Joint crack sealing	0	—	—	—	1	20	20	20	NC
WNF		5	13	20	19	2	20	20	20	1
DF		0	—	—	—	1	20	20	20	NC
DNF		0	—	—	—	2	17	20	19	NC
WF	Joint undersealing	0	—	—	—	1	20	20	20	NC
WNF		2	20	20	20	2	20	20	20	0
DF		0	—	—	—	1	20	20	20	NC
DNF		0	—	—	—	2	17	20	19	NC
—Indicates no data. Min = Minimum. Max = Maximum. Avg = Average. NC = Could not be compared.

 

Table 94. Impacts of various maintenance treatments and control section on pavement performance in terms of RSP based on transverse cracking.

Climatic Region	Treatment Type	RFP (Year)								Difference in RSP (Year)
		Test Sections				Control Sections
		Number of Test Sections	Min	Max	Avg	Number of Test Sections	Min	Max	Avg
WF	Joint crack sealing	1	20	20	20	2	11	20	16	4
WNF		4	6	20	14	3	20	20	20	6
DF		1	19	19	19	1	20	20	20	1
DNF		0	—	—	—	1	14	14	14	NC
WF	Joint undersealing	0	—	—	—	2	11	20	16	NC
WNF		2	1	20	11	3	20	20	20	9
DF		0	—	—	—	1	20	20	20	NC
DNF		0	—	—	—	1	14	14	14	NC
—Indicates no data. Min = Minimum. Max = Maximum. Avg = Average. NC = Could not be compared.

 

IRI

The calculated minimum, maximum, and average RFPs based on IRI data for the SPS-4 test sections that were subjected to the same treatment type and for the associated control sections are listed in table 92. The data in the table indicate the following:

• Eight SPS-4 test sections in the WF region were subjected to joint and crack sealing and accepted for analyses. The minimum, maximum, and average RFPs of the eight SPS-4 test sections were 10, 20, and 17 years, respectively. In addition, there were eight control sections with minimum, maximum, and average RFPs of 8, 20, and 17 years, respectively. Thus, the difference between the average RFPs of the treated test sections and the control sections was 0 years. That is, joint crack sealing had no impact on pavement performance in the WF region.
  
  
• The average RFP of the 10 treated SPS-4 test sections located in the WNF region was 3 years longer than the average RFP of the 11 control sections located in the same region.
  
  
• The average RFP of the four treated SPS-4 test sections located in the DF region was 3 years shorter than the average RFP of the two control sections located in the same region.
  
  
• The average RFP of the two treated SPS-4 test sections located in the DNF region was 5 years shorter than the average RFP of the two control sections located in the same region.
  
  
• The joint undersealing treatment of the SPS-4 test sections in the WNF, DF, and DNF regions caused greater pavement roughness, and consequently, the average RFPs of the control sections in the three regions were substantially shorter than the test sections.

The main reason for the differences between the average RFPs of the test sections and the control sections is that the conditions of the control sections were not representative of the conditions of the test sections when they were subjected to treatments. For example, the IRI obtained from the first survey performed on the treated test section 06B420 was 156 inches/mi (2.4 m/km) while the IRI of the control section 06B430 was 123.5 inches/mi (1.9 m/km). Because the magnitude and the rates of deterioration of the two test sections were different, they precipitated differences in their RFPs.

Longitudinal Cracking

The calculated minimum, maximum, and average RSPs based on longitudinal cracking data for the SPS-4 test sections that were subjected to the same treatment type and for the associated control sections are listed in table 93. The data in the table indicate that neither treatment had any impact on the average RFPs of the SPS-4 test sections located in the WNF region. No test or control sections are located in the other three climatic regions.

Transverse Cracking

The calculated minimum, maximum, and average RSPs based on transverse cracking of the SPS‑4 test sections that were subjected to the same treatment type and for the associated control sections are listed in table 94. The data in the table indicate the following:

• Joint and crack sealing had a positive impact on pavement performance in the WF region. The RFP of the one SPS-4 test section was 4 years longer than the average RFP of the two control sections, whereas, the same treatment caused losses in the average RFPs of the SPS-4 test sections located in the WNF and DF regions.
  
  
• The two SPS-4 test sections located in the WNF region and subjected to joint undersealing performed worse than the three control sections by 9 years.

Summary, Conclusions, and Recommendations for LTTP SPS-4

The available data in the LTPP database regarding the LTPP SPS-4 experiment were downloaded, organized, and analyzed. The intent was to study the impact of two maintenance treatments, joint and crack sealing (410) and joint undersealing (420), on pavement performance.

When the data were separated based on traffic levels, the number of test sections that were available for analyses in each traffic level was statistically insignificant. Therefore, the data were grouped based on the two maintenance treatment types and the four climatic regions. For each group, the minimum, maximum, and average RFPs and RSPs for the test and control sections were calculated and are listed in table 92 through table 94. The impacts of the two maintenance treatments in each climatic region were presented in the section following the tables. Based on the results of the analyses, the following conclusions were drawn:

• On average, in terms of IRI, joint and crack sealing treatment had no impact on pavement performance in the WF region, a positive impact in the WNF region, and a negative impact in the DF and DNF regions.
  
  
• On average, in terms of IRI, joint undersealing treatment had a negative impact on pavement performance in the WNF, DF, and DNF regions.
  
  
• On average, the two maintenance treatments had no impact on pavement performance in terms of longitudinal cracking in the WNF region.
  
  
• Joint and crack sealing treatment had a positive impact on pavement performance in the WF region and a negative impact in the WNF region.
  
  
• Joint undersealing treatment had no impact on the pavement performance in terms of transverse cracking in the WNF region.

In summary, the research team concluded that joint and crack sealing was effective in the WF region and not effective in the other three climatic regions, and joint undersealing was not effective in any region.

IMPACTS OF REHABILITATION TREATMENTS ON PAVEMENT CONDITION AND DISTRESS USING THE LTPP SPS-6 TEST SECTIONS

The main objective of the SPS-6 experiment was to examine the effects of various rehabilitation treatments on the performance of rigid pavement test sections. The 14 SPS-6 test sites were initiated between 1989 and 1998 and are distributed across the United States and Canada. Each SPS-6 test site consisted of 1 control section and 7 treated test sections for a total of 112 test sections. Each of the seven treated sections was subjected to one of the following rehabilitation actions (note that the numbers in parenthesis are the LTPP designation of the rehabilitation actions):

• Minimum restoration (602).
  
  
• Minimum restoration with 4-inch (102-mm) AC overlay (603).
  
  
• Minimum restoration with 4-inch (102-mm) AC overlay and sawed and sealed joints in the AC (604).
  
  
• Maximum restoration (605).
  
  
• Maximum restoration with 4-inch (102-mm) AC overlay (606).
  
  
• Crack, break, and seat with 4-inch (102-mm) AC overlay (607).
  
  
• Crack, break, and seat with 8-inch (204-mm) AC overlay (608).

The minimum restoration action included limited patching, crack sealing, and joint stabilization. Further, diamond grinding was performed when faulting was considered too high. Maximum restoration included subsealing, subdrainage, joint repair and sealing, full-depth repairs and load transfer restoration, and diamond grinding. Cracking and seating was used for JPCP test sections while breaking and seating was performed for JRCP test sections.

For each SPS-6 test section subjected to one of the previously listed rehabilitation actions, the time-series pavement condition and distress data (collected after the rehabilitation action was taken and before the next treatment was applied) were used to calculate the RFPs and RSPs of that section. Thus, RFPs and RSPs expressed the pavement service period between rehabilitation and the time when the pavement condition or distress reached the prespecified threshold values. Similarly, the RFPs and RSPs of the control sections were also calculated. For each pavement condition (IRI) and distress type (rut depth and alligator, longitudinal, and transverse cracking), the treatment benefits were expressed in terms of the following:

• RFP or RSP of the treated pavement section.
  
  
• The difference in RFP or RSP of the treated pavement section and RFP or RSP of the associated control section. This difference was labeled CFP or CSP.

Results of the analyses of the treatment benefits are listed in table 95 through table 99 based on two climatic regions (no test sections were present in the DF and DNF regions), pavement type, and pavement condition and distress type. The data in the tables are discussed in the following subsections per pavement condition and distress type.

Table 95. RFP of control sections and the impact of treatment types on pavement performance in terms of RFP based on IRI.

Climatic Region	Pavement Type	State (Code)	Control Section RFP (Year)	Minimum Restoration and No AC Overlay		Minimum Restoration and AC Overlay				Maximum Restoration and No AC Overlay		Maximum Restoration and 4-inch AC Overlay		Crack/Break and Seat and AC Overlay
						4 inches		4 inches With SS						4 inches		8 inches
				RFP	CFP	RFP	CFP	RFP	CFP	RFP	CFP	RFP	CFP	RFP	CFP	RFP	CFP
WF	JPCP	AZ (04)	ND	ND	—	18	—	20	—	ND	—	20	—	20	—	20	—
		IN (18)	ND	NS	—	20	—	20	—	NS	—	20	—	14	—	20	—
		MO (29)	ND	20	—	20	—	10	—	16	—	15	—	20	—	20	—
		SD (46)	ND	ND	—	ND	—	ND	—	ND	—	ND	—	ND	—	ND	—
		Average	—	20	—	19	—	17	—	16	—	18	—	18	—	20	—
	JRCP	IL (17)	7	20	13	20	13	20	13	13	6	ND	—	20	13	20	13
		IA (19)	ND	ND	—	ND	—	ND	—	20	—	20	—	20	—	20	—
		MI (26)	11	ND	—	20	9	NS	—	3	8	20	9	NS	—	20	9
		MO (29)	ND	ND	—	20	—	20	—	ND	—	20	—	ND	—	20	—
		PA (42)	ND	ND	—	19	—	20	—	ND	—	19	—	20	—	20	—
		Average	9	20	11	20	11	20	11	12	3	20	11	20	11	20	11
WNF	JPCP	AL (01)	0	20	20	20	20	20	20	20	20	20	20	ND	—	20	20
		AR (05)	ND	20	—	20	—	20	—	ND	—	20	—	20	—	20	—
		CA (06)	0	ND	—	15	15	ND	—	7	7	ND	—	16	16	20	20
		TN (47)	ND	15	—	20	—	13	—	ND	—	20	—	ND		20	—
		Average	0	18	18	19	19	18	18	14	14	20	20	18	18	20	20
	JRCP	OK (40)	ND	ND	—	ND	—	ND	—	ND	—	ND	—	ND	—	ND	—
— Indicates could not be calculated. 1 inch = 25.4 mm. SS = saw and seal of joints. ND = no data.

 

Table 96. Impact of various treatments and control section on pavement performance in terms of RFP/RSP based on rut depth.

Climatic Region	Pavement Type	State (Code)	Control Section RSP (Year)	Minimum Restoration and No AC Overlay		Minimum Restoration and AC Overlay				Maximum Restoration and No AC Overlay		Maximum Restoration and 4-inch AC Overlay		Crack/Break and Seat and AC Overlay
						4 inches		4 inches With SS						4 inches		8 inches
				RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP
WF	JPCP	AZ (04)	N/A	N/A	—	20	—	20	—	N/A	—	NS	—	20	—	20	—
		IN (18)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	20	—	20	—
		MO (29)	N/A	N/A	—	NS	—	NS	—	N/A	—	NS	—	NS	—	NS	—
		SD (46)	N/A	N/A	—	ND	—	ND	—	NA	—	ND	—	ND	—	ND	—
		Average	—	—	—	20	—	20	—	—	—	20	—	20	—	20	—
	JRCP	IL (17)	N/A	N/A	—	20	—	20	—	N/A	—	ND	—	NS	—	NS	—
		IA (19)	N/A	N/A	—	NS	—	20	—	N/A	—	NS	—	NS	—	20	—
		MI (26)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	20	—	20	—
		MO (29)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	ND	—	20	—
		PA (42)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	20	—	20	—
		Average	—	—	—	20	—	20	—	—	—	20	—	20	—	20	—
WNF	JPCP	AL (01)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	20	—	20	—
		AR (05)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	20	—	20	—
		CA (06)	N/A	N/A	—	20	—	20	—	N/A	—	ND	—	20	—	20	—
		TN (47)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	ND	—	20	—
		Average	—	—	—	20	—	20	—	—	—	20	—	20	—	20	—
	JRCP	OK (40)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	20	—	20	—
— Indicates could not be calculated. 1 inch = 25.4 mm. SS = Saw and seal of joints. ND = No data. N/A = Not applicable. NS = Negative model slope (pavement condition and/or distress improving over time with no treatment).

 

Table 97. Impact of various treatments and control section on pavement performance in terms of RSP based on alligator cracking.

Climatic Region	Pavement Type	State (Code)	Control Section RSP (Year)	Minimum Restoration and No AC Overlay		Minimum Restoration and AC Overlay				Maximum Restoration and No AC Overlay		Maximum Restoration and 4-inch AC Overlay		Crack/Break and Seat and AC Overlay
						4 inches		4 inches With SS						4 inches		8 inches
				RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP
WF	JPCP	AZ (04)	N/A	N/A	—	13	—	20	—	N/A	—	19	—	19	—	20	—
		IN (18)	N/A	N/A	—	20	—	13	—	N/A	—	11	—	12	—	12	—
		MO (29)	N/A	N/A	—	ND	—	15	—	N/A	—	19	—	19	—	20	—
		SD (46)	N/A	N/A	—	ND	—	ND	—	N/A	—	ND	—	ND	—	ND	—
		Average	—	—	—	17	—	16	—	—	—	16	—	17	—	17	—
	JRCP	IL (17)	N/A	N/A	—	5	—	13	—	N/A	—	ND	—	ND	—	18	—
		IA (19)	N/A	N/A	—	ND	—	8	—	N/A	—	8	—	8	—	10	—
		MI (26)	N/A	N/A	—	20	—	ND	—	N/A	—	10	—	ND	—	20	—
		MO (29)	N/A	N/A	—	ND	—	20	—	N/A	—	ND	—	ND	—	16	—
		PA (42)	N/A	N/A	—	20	—	ND	—	N/A	—	ND	—	20	—	ND	—
		Average	—	—	—	15	—	14	—	—	—	9	—	14	—	16	—
WNF	JPCP	AL (01)	N/A	N/A	—	9	—	15	—	N/A	—	ND	—	3	—	7	—
		AR (05)	N/A	N/A	—	18	—	16	—	N/A	—	18	—	20	—	20	—
		CA (06)	N/A	N/A	—	7	—	ND	—	N/A	—	ND	—	5	—	7	—
		TN (47)	N/A	N/A	—	ND	—	12	—	N/A	—	ND	—	ND	—	ND	—
		Average	—	—	—	11	—	14	—	—	—	18	—	9	—	11	—
	JRCP	OK (40)	N/A	N/A	—	20	—	20	—	N/A	—	20	—	5	—	9	—
— Indicates could not be calculated. 1 inch = 25.4 mm. SS = Saw and seal of joints. ND = No data. N/A = Not applicable.

 

Table 98. Impact of various treatments and control section on pavement performance in terms of RSP based on longitudinal cracking.

Climatic Region	Pavement Type	State (Code)	Control Section RSP (Year)	Minimum Restoration and No AC Overlay		Minimum Restoration and AC Overlay				Maximum Restoration and No AC Overlay		Maximum Restoration and 4-inch AC Overlay		Crack/Break and Seat and AC Overlay
						4 inches		4 inches With SS						4 inches		8 inches
				RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP
WF	JPCP	AZ (04)	ND	ND	—	7	—	12	—	ND	—	13	—	10	—	13	—
		IN (18)	ND	19	—	6	—	12	—	20	—	14	—	15	—	10	—
		MO (29)	20	ND	—	10	10	6	14	13	7	9	11	10	10	10	10
		SD (46)	ND	ND	—	ND	—	ND	—	ND	—	ND	—	ND	—	ND	—
		Average	20	19	1	8	12	10	10	17	3	12	8	12	8	11	9
	JRCP	IL (17)	13	ND	—	20	7	12	1	ND	—	ND	—	20	7	17	4
		IA (19)	ND	ND	—	ND	—	7	—	ND	—	3	—	0	—	1	—
		MI (26)	19	ND	—	10	9	ND	—	NS	—	10	9	9	10	9	10
		MO (29)	ND	ND	—	ND	—	19	—	ND	—	20	—	ND	—	20	—
		PA (42)	ND	ND	—	14	—	15	—	ND	—	14	—	14	—	17	—
		Average	16	—	—	15	1	13	3	—	—	12	4	11	5	13	3
WNF	JPCP	AL (01)	ND	20	—	5	—	6	—	ND	—	5	—	7	—	20	—
		AR (05)	ND	ND	—	10	—	10	—	ND	—	12	—	9	—	9	—
		CA (06)	ND	ND	—	6	—	7	—	ND	—	7	—	5	—	5	—
		TN (47)	ND	20	—	6	—	5	—	ND	—	5	—	ND	—	7	—
		Average	—	20	—	7	—	7	—	—	—	7	—	7	—	10	—
	JRCP	OK (40)	ND	ND	—	3	—	3	—	ND	—	3	—	3	—	3	—
— Indicates could not be calculated. 1 inch = 25.4 mm. SS = Saw and seal of joints. ND = No data.

 

Table 99. Impact of various treatments and control section on pavement performance in terms of RSP based on transverse cracking.

Climatic Region	Pavement Type	State (State Code)	Control Section RSP (Year)	Minimum Restoration and No AC Overlay		Minimum Restoration and AC Overlay				Maximum Restoration and No AC Overlay		Maximum Restoration and 4-inch AC Overlay		Crack/Break and Seat and AC Overlay
						4 inches		4 inches With SS						4 inches		8 inches
				RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP	RSP	CSP
WF	JPCP	AZ (04)	ND	ND	—	3	—	0	—	ND	—	7	—	8	—	12	—
		IN (18)	ND	ND	—	3	—	0	—	ND	—	3	—	3	—	16	—
		MO (29)	20	20	0	12	8	0	20	20	0	9	11	11	9	10	10
		SD (46)	ND	ND	—	ND	—	ND		ND	—	ND	—	ND	—	ND	—
		Average	20	20	0	6	14	0	20	20	0	6	14	7	13	13	7
	JRCP	IL (17)	5	0	5	20	15	20	15	0	5	ND	—	ND	—	20	15
		IA (19)	ND	ND	—	ND	—	NS		ND	—	NS	—	20	—	14	—
		MI (26)	0	ND	—	19	19	ND		0	0	15	15	14	14	12	12
		MO (29)	ND	ND	—	ND	—	NS		ND	—	20	—	ND	—	20	—
		PA (42)	ND	ND	—	20	—	NS		ND	—	20	—	20	—	ND	—
		Average	3	0	3	20	17	20	17	0	3	18	15	18	15	17	14
WNF	JPCP	AL (01)	20	20	0	7	13	0	20	12	8	5	15	4	16	20	0
		AK (05)	ND	ND	—	8	—	0	—	ND	—	8	—	10	—	13	—
		CA (06)	ND	ND	—	6	—	ND	—	ND	—	ND	—	11	—	12	—
		TN (47)	ND	20	—	13	—	1	—	ND	—	11	—	ND	—	ND	—
		Average	20	20	0	9	11	0	20	12	8	8	12	8	12	15	5
	JRCP	OK (40)	ND	ND	—	12	—	17	—	ND	—	17	—	4	—	20	—
— Indicates could not be calculated. 1 inch = 25.4 mm. SS = Saw and seal of joints. ND = No data. NS = Negative model slope (pavement condition and/or distress improving over time with no treatment).

 

IRI

The data listed in table 95 indicate the following:

• Although the RFP and CFP of some treated pavement sections are listed in the table, the results were based on only one test section and one control section. Hence, no substantial discussion and/or conclusion could be made.
  
  
• Based on the limited number of test sections in each treatment type, the following appeared to be true, on average:
  
  
  • The maximum restoration and no AC overlay treatment type yielded the lowest RFP. This could be related to the treatment type or more likely the construction quality that yielded high pavement roughness.
    
    
  • The impact of rigid pavement type and climatic region on the performance of the treated test sections was similar.

Rut Depth

The data listed in table 96 indicate the following:

• Although the test sections that received AC overlay has rut depth measurements available in the LTPP database, the PCC control sections were not subjected to AC overlay and hence did not have rut depth data. Therefore, no CFPs/CSPs could be calculated.
  
  
• Once again, although RFPs/RSPs of most treated pavement sections are listed in the table, the data in each category (each cell in the table) were based on only one test section. Nevertheless, the data in the table indicate that RFPs/RSPs of all treated pavement sections, where a minimum of three data points were collected, was 20 years, regardless of the treatment type, pavement type, or climatic region.

Alligator Cracking

The data listed in table 97 indicate the following:

• The LTPP database had no alligator cracking data for any of the control sections. Once again, the reason was that the control sections were rigid pavement, while the test sections were composite pavements.
  
  
• The reported alligator cracking data on the test sections were highly likely top-down cracking. The reason was that in composite pavements, surface tensile stress and strain due to pavement-tire interaction was greater than the tensile stress and strain at the bottom of the AC overlay. Nevertheless, RSPs of most of the treated pavement sections listed in table 97 were based on only one test section per treatment type, pavement type, and climatic region. The data could not be compared with the control sections to extract treatment benefits because of the different pavement types. However, the differential benefits of the various treatments could be obtained by studying the minimum, maximum, and average values of RSP. The data in the table indicate the following:
  
  
  • RSPs of the test sections subjected to minimum restoration and 4-inch (102-mm) AC overlay ranged from a low of 5 years to a high of 20 years, with an average of about 14 years.
    
    
  • RSPs of the test sections subjected to minimum restoration, sawing and sealing the joints, and 4-inch (102-mm) AC overlay ranged from a low of 5 years to a high of 20years, with an average of about 15 years.
    
    
  • RSPs of the test sections subjected to maximum restoration and 4-inch (102-mm) AC overlay ranged from a low of 8 years to a high of 20 years, with an average of about 15 years.
    
    
  • RSPs of the test sections subjected to crack, break and seat, and 4-inch (102-mm) AC overlay ranged from a low of 5 years to a high of 20 years, with an average of about 15 years.
    
    
  • RSPs of the test sections subjected to crack, break, and seat and 8-inch (203-mm) AC overlay ranged from a low of 7 years to a high of 20 years, with an average of about 15 years.

These observations indicate that the pavement performance of the five treatments was almost the same and independent of pavement type and climatic region.

Longitudinal Cracking

The data listed in table 98 indicate the following:

• The LTPP database contained three or more time-series data points for only three control sections. The other 11 sections either had fewer than three data points or the control section was treated before three data points were collected.
  
  
• It appeared that none of treatment types applied to JPCP and JRCP test sections located in the WF region were effective. The performance of the treated sections was less than the performance of the control sections.
  
  
• For JPCP test sections located in the WNF region, it appeared that the minimum restoration and no AC overlay treatment yielded the highest RSP (20 years), while the crack and break and seat and 8-inch AC overlay yielded an RSP of 10 years. RSPs of the test sections that received each of the other four treatments were 7 years.

Transverse Cracking

The data listed in table 99 indicate the following:

• For the JRCP test section located in Illinois (WF region), the minimum restoration and no AC overlay treatment appeared not to address the transverse cracking problem; the RSP of the treated test section is 0 years. Further, RSPs of two test sections located in Illinois and Michigan and subjected to maximum restoration and no AC overlay treatment were also 0 years. The data from this limited number of test sections suggested that neither the minimum nor the maximum restoration with no overlay treatments addressed transverse cracking problems in JRCP test sections, or the treatment construction quality was not adequate, or a combination thereof. On the other hand, the two treatments appeared to be the right treatment for the four JPCP test sections located in the WF (two sections in Missouri) and WNF regions (two sections in Alabama).
  
  
• The other three treatments—minimum and maximum restoration with 4-inch (102-mm) AC overlay—appeared to be the right treatment for transverse cracking of JRCP test sections located in the WF region.

Summary, Conclusions, and Recommendations for LTPP SPS-6

The available data in the LTPP database Standard Data Release 28.0 regarding the LTPP SPS-6 experiment were downloaded, organized, and analyzed. The intent was to study the impact of seven maintenance treatments on pavement performance. Each of the 7 test sections of each of the 14 test sites was subjected to certain treatments. The measured condition and distress data for each test site and control section were analyzed, and RFP, RSP, CFP, and CSP were calculated. The results were then grouped per pavement type and climatic region for further analyses. Unfortunately, the IRI and distress data for many control sections and for some test sections did not support the analyses because of either the lack of three data points or improvement in the pavement condition and/or distress over time without the application of treatments. Consequently, the results for only a few test sections could be compared. Based on the limited number of test and control sections, the following conclusions were drawn:

• RFP values of the treated pavement sections were independent of pavement type and climatic region.
  
  
• The pavement performance based on rut depth of treated test sections was independent of the treatment type, pavement type, and climatic region.
  
  
• The alligator cracking data in the database were highly likely an advanced form of top-down cracking (top-down cracks are fatigue cracks that initiate at the pavement surface and, over time, propagate downward) where the transverse and longitudinal cracks resembled alligator cracking.
  
  
• The performance of the test sections in terms of longitudinal cracking was worse after subjecting the section to any of the seven treatment types.
  
  
• Minimum and maximum pavement restoration with no AC overlay treatments did not improve the performance of the JRCP test sections.

It should be noted that each of these conclusions should be accepted with cautious because they were based on the results of a few and sometimes on only one test section.

IMPACTS OF BONDED CONCRETE OVERLAYS ON PAVEMENT PERFORMANCE USING THE LTPP SPS-7 TEST SECTIONS

The main objective of the SPS-7 experiment is to study the effects of bonded concrete overlay thickness, surface preparation before concrete overlay, and the use of cement grout on the performance of PCC pavements. Four SPS-7 test sites were initiated between 1990 and 1992. Three of the four sites consisted of CRCP test sections while the fourth site consisted of JPCP test sections. Each of the four test sites had eight test sections and one control section, except the test site in Louisiana, where no control section was included. The eight test sections were subjected to one of the following treatments (the numbers in parenthesis are the LTPP designation of the treatment):

• Three-inch (76-mm) concrete overlay with milling and grouting (702).
  
  
• Three-inch (76-mm) concrete overlay with milling (703).
  
  
• Three-inch (76-mm) concrete overlay with shot blasting (704).
  
  
• Three-inch (76-mm) concrete overlay with shot blasting and grouting (705).
  
  
• Five-inch (127-mm) concrete overlay with shot blasting and grouting (706).
  
  
• Five-inch (127-mm) concrete overlay with shot blasting (707).
  
  
• Five-inch (127-mm) concrete overlay with milling (708).
  
  
• Five-inch (127-mm) concrete overlay with milling and grouting (709).

For each test section that was subjected to one of these treatments, the available time-series pavement condition and distress data from the time of treatment to that of the next treatment were used to calculate the RFP and RSP of that section. Hence RFP and RSP describe the time period between the treatment construction and the time when the pavement condition or distress reached the prespecified threshold values. The RFPs and RSPs of the control sections were also calculated. For each pavement condition (IRI) and distress type (longitudinal and transverse cracking), the treatment benefits were calculated based on the following:

• The RFP and RSP of each treated test section.
  
  
• The difference in the RFP or RSP of the treated test section and the RFP or RSP of the associated control section. The difference was labeled CFP and CSP.

Results of the analyses are listed in table 100 through table 102 and discussed in the following subsections based on pavement condition and distress type. It should be noted that, for each of the CRCP test sections, the total transverse crack length was calculated as the sum of half of the cumulative length of low severity transverse cracks, the total length of medium severity cracks, and the total length of high severity transverse cracks. The reason was that the signature of CRCP is the tightly spaced transverse cracks (also called shrinkage cracks). Some of these transverse cracks may open up over time, connect, and produce punch-outs. After careful observations of the CRCP transverse crack data, it was observed that for most CRCP test sections, the total length of the low-severity transverse cracks reported in the database exceeded the crack saturation point. Therefore, it was assumed that about half of the total length of the reported low-severity transverse cracks was open enough to be considered in the analyses. The other half were very tight shrinkage cracks.

Table 100. Impact of bonded concrete overlays on pavement performance in terms of RFP based on IRI.

Climatic Region	Existing Pavement Type	State (Code)	Control Section RFP (Year)	RFP and CFP (B1) of Treated Test Sections (Years)
				Thin Bonded Overlay									Thick Bonded Overlay
				Milling				Shot Blasting					Milling				Shot Blasting
				G		NG		G		NG			G		NG		G		NG
				RFP	B1	RFP	B1	RFP	B1		RFP	B1	RFP	B1	RFP	B1	RFP	B1	RFP	B1
WF	CRCP	Iowa (19)	20	20	0	20	0	NS	—		NS	—	20	0	20	0	NS	—	20	0
		Minnesota (27)	ND	20	—	20	—	20	—		20	—	20	—	20	—	20	—	17	—
	JPCP	Missouri (29)	10	20	10	16	6	20	10		10	0	20	10	20	10	19	9	20	10
WNF	CRCP	Louisiana (22)	NCS	20	—	20	—	20	—		20	—	20	—	20	—	20	—	NS	—
—Indicates could not be calculated. G = Grouting. NG = No grouting. NCS = No control section. ND = No data, no distress is observed, or fewer than three data points. NS = Negative slope. Thin = 3 inches (76 mm). Thick = 5 inches (127 mm). B1 = CFP.

 

Table 101. Impact of bonded concrete overlays on pavement performance in terms of RSP based on longitudinal cracking.

Climatic Region	Existing Pavement Type	State (State Code)	Control Section RFP (Year)	RSP and CSP (B1) of Treated Test Sections (Years)
				Thin Bonded Overlay								Thin Bonded Overlay
				Milling				Milling				Milling				Milling
				G		NG		G		NG		G		NG		G		NG
				RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1
WF	CRCP	Iowa (19)	ND	ND	—	20	—	ND	—	ND	—	ND	—	NS	—	ND	—	ND	—
		Minnesota (27)	ND	ND	—	ND	—	ND	—	20	—	20	—	ND	—	20	—	11	—
	JPCP	Missouri (29)	20	ND	—	18	2	20	0	20	0	20	0	20	0	13	7	20	0
WNF	CRCP	Louisiana (22)	NCS	NS	—	ND	—	ND	—	ND	—	ND	—	20	—	ND	—	20	—
—Indicates could not be calculated. G = Grouting. NG = No grouting. NCS = No control section. ND = No data, no distress is observed, or fewer than three data points. NS = Negative slope. Thin = 3 inches (76 mm). Thick = 5 inches (127 mm). B1 = CFP.

 

Table 102. Impact of bonded concrete overlays on pavement performance in terms of RSP based on transverse cracking.

Climatic Region	Existing Pavement Type	State (State Code)	Control Section RFP (Year)	RSP and CSP (B1) of Treated Test Sections (Years)
				Thin Bonded Overlay								Thin Bonded Overlay
				Milling				Milling				Milling				Milling
				G		NG		G		NG		G		NG		G		NG
				RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1	RSP	B1
WF	CRCP	Iowa (19)	ND	9	—	7	—	6	—	6	—	0	—	0	—	3	—	7	—
		Minnesota (27)	ND	0	—	0	—	0	—	0	—	0	—	ND	—	0	—	2	—
	JPCP	Missouri (29)	20	0	20	11	9	9	11	0	20	0	20	0	20	0	20	0	20
WNF	CRCP	Louisiana (22)	NCS	0	—	0	—	2	—	0		ND	—	0	—	0	—	0	—
—Indicates could not be calculated. G = Grouting. NG = No grouting. NCS = No control section. ND = No data, no distress is observed, or fewer than three data points. NS = Negative slope. Thin = 3 inches (76 mm). Thick = 5 inches (127 mm). B1 = CFP.

 

IRI

Table 100 lists RFPs and CFPs of all LTPP CRCP test sections located in Iowa, Minnesota, and Louisiana and the JPCP test sections located in Missouri. The data in the table indicate the following:

• The measured time-dependent IRI data of three of the eight CRCP test sections in Iowa showed improvement in the IRI over time (negative slope) without the application of any treatment. Hence, RFP and CFP of those three test sections were not calculated.
  
  
• RFPs of the other 21 CRCP test sections in Iowa, Minnesota, and Louisiana were about 20 years (20 years for 20 sections and 17 years for 1 section in Minnesota). That is, the data indicate that the performance of the treated CRCP test sections was independent of the eight treatment types and the two climatic regions.
  
  
• RFPs and the CFPs of the eight JPCP test sections located in Missouri appeared to be related to the treatment type. RFPs of the two test sections that were not grouted and subjected to a 3-inch (76-mm) concrete overlay with milling (703) or with shot blasting (704) are 16and 10 years, respectively. These RFPs were 20 and 50 percent lower than the other two test sections that were grouted and subjected to 3-inch (76-mm) overlay and the four test sections that were subjected to 5-inch (127-mm) concrete overlays with and without grouting.
  
  
• The maximum CFP of the JPCP test sections (10 years) is mainly due to the low RFP of the control section (10 years).

Longitudinal Cracking

Table 101 lists RSPs and CSPs of all LTPP CRCP test and control sections located in Iowa, Minnesota, and Louisiana, and the JPCP test sections located in Missouri. The data in the table indicate the following:

• Only one of the eight test sections in Iowa had adequate time-series longitudinal data to be analyzed. The RSP of that test section was 20 years. Another test section showed improvement in the length of longitudinal cracking over time without the application of any treatment (negative slope). The LTPP database contained 0.1-ft (30-mm)-long measured longitudinal cracking over time for the other six test sections and for the control section.
  
  
• The RSPs and CSPs for four test sections in Minnesota are listed in table 101. Once again, The LTPP database contained 0.1-ft (30-mm)-long measured longitudinal cracking over time for three test sections and for the control section and only two data points for one test section.
  
  
• The RSPs and CSPs for two test sections in Louisiana are listed in table 101. Once again, the LTPP database contained 0.1-ft (30-mm)-long measured longitudinal cracking over time for four test sections and only two data points for one test section. The data showed improvement over time in the length of longitudinal cracking without the application of any treatment.
  
  
• The RSPs and CSPs of six JPCP test sections located in Missouri appear to be independent of the treatment type The RSP of one test section that was subjected to 5‑inch (127-mm) concrete overlay with shot blasting and grouting was 13 years, about 7years shorter than the RSPs of the other test sections. This could be the exception and not the rule. Stated differently, no decision could be or should be drawn based on only one section.

Transverse Cracking

Table 102 lists the RSP and the CSP values of most LTPP CRCP test sections located in Iowa, Minnesota, and Louisiana and the JPCP test sections located in the State of Missouri. The LTPP database did not contain adequate data except for two CRCP test sections, one located in Minnesota and the other in Louisiana. The data in table 102 indicated that none of the eight treatments in the two climatic regions were successful in treating transverse cracking problems in CRCP. The time-series transverse cracking data indicated that the RSP value was 0 years for two test sections in Iowa, six test sections in Minnesota, and six test sections in Louisiana. Further, the RSP of only one test section in each of the two States was 2 years, while the RSP of six test sections in Iowa ranged from 3 to 9 years.

Summary, Conclusions, and Recommendations for LTPP SPS-7

The LTPP SPS-7 experiment was designed to study the effects of bonded concrete overlay thickness, surface preparation before concrete overlay, and the use of cement grout on the performance of PCC pavements. Such study would be based on comparison between the performance of the test sections and the performance of compatible control sections. The pavement condition and distress data for each test and control section were downloaded from the LTPP database, organized, and analyzed to obtain the performance of the sections. Results of the analyses are listed in table 100 through table 102. Based on the results of the analyses, the following conclusions were drawn:

• The IRI-based performance of the treated CRCP test sections was independent of the eight treatment types and the two climatic regions.
  
  
• The performance of the JPCP test sections subjected to 3-inch (76-mm) concrete overlay with milling (703) or with shot blasting (704) treatments appeared to be lower than the performance of the other JPCP test sections subjected to the other six treatments.
  
  
• Because of lack of an adequate number of data points in the LTPP database, no specific conclusions could be drawn regarding longitudinal cracking performance.
  
  
• None of the eight treatments were effective to treat transverse cracking problems of the CRCP test sections.

IMPACTS OF PAVEMENT TREATMENTS ON PAVEMENT PERFORMANCE USING THE LTPP GPS-7 TEST SECTIONS

The GPS-7 pavement test sections are composites that were overlain prior to their assignment to the LTPP Program. The experiment also includes rigid pavement test sections that were moved from other LTPP experiments after they were subjected to AC overlay or existing composite pavement test sections that were subjected to mill and fill. The test sections in the GPS-7 experiment are classified as GPS-7A, -7B, -7C, -7D, -7F, and -7S. The following explains each of the classifications:

• GPS-7A: The test sections under this classification were part of the original LTPP design. They were subjected to AC overlay prior to their assignment to the LTPP Program.
  
  
• GPS-7B: The test sections under this classification were also part of the original LTPP design. They were subjected to AC overlay following assignment to the LTPP Program.
  
  
• GPS-7C, -7D, -7F, and -7S: The test sections under these classifications did not have an experimental design associated with them. They were moved to GPS-7C, -7D, -7F, or -7S classification from other LTPP experiments after they were subjected to rehabilitation actions. The specific classification in the four GPS-7 experiments depended on the type of pavement rehabilitation detailed as follows:
  
  
  • If the rigid pavement test sections from other LTPP experiments were overlain with virgin AC mixes, they were moved to the GPS-7B classification.
    
    
  • If the rigid pavement test sections from other LTPP experiments were overlain or if the existing composite pavement test sections were overlain again using recycled AC mixes, they were moved to the GPS-7C classification.
    
    
  • If the existing composite pavement test sections were overlain again using conventional AC mixes, they were moved to the GPS-7D classification.
    
    
  • If the rigid pavement test sections from other LTPP experiments were subjected to crack and break and seat before being overlain using virgin or recycled AC mixes, they were moved to the GPS-7F classification.
    
    
  • If the existing composite pavement test sections from other LTPP experiments were subjected to mill and fill using virgin or recycled AC mixes, they were moved to the GPS-7S classification.

Unfortunately, the number of rigid and composite pavement test sections that had more than three condition and/or distress data points before they were subjected to overlay or mill-and-fill treatments was extremely low. Given that the behavior of rigid pavement test sections would be much different than that of a composite pavement test sections, they could not be grouped to increase the number of test sections for analyses. However, the LTPP test sections in the GPS-7 experiment that had three or more after treatment time-series pavement condition and/or distress data points were grouped according to the following variables:

• Two treatment types (AC overlay and mill and fill).
  
  
• AC mix type (virgin and recycled).
  
  
• Thickness types (thin ≤ 2.5 inches (63.5 mm) and thick > 2.5 inches (63.5 mm)).
  
  
• Four climatic regions (WF, WNF, DF, and DNF).
  
  
• One pavement condition (IRI).
  
  
• Four pavement distress types (rut depth, and alligator, longitudinal, and transverse cracking).

After grouping, the data were analyzed to assess, in each climatic region, the impacts of treatment type, AC mix type, and thickness on the calculated RFP and RSP based on IRI, rut depth, and cracking. It should be noted that the LTPP database contained no before treatment pavement condition and distress data for any test section. Therefore, only the RFP or RSP of the pavement sections were calculated. For each pavement condition and distress type, the average RFPs and/or RSPs of the test sections located in the same climatic region were calculated and are listed in table 103 through table 107. The data in the five tables are discussed in the following sections per pavement condition and distress type.

Table 103. Impacts of various treatment types on RFP of the test sections based on IRI.

Treatment Type	Mix Type	Thickness	Number of Test Sections and RFP Values in the Designated Climatic Region
			WF		WNF		DF		DNF
			No.	RFP (Year)	No.	RFP (Year)	No.	RFP (Year)	No.	RFP (Year)
Overlay	Virgin	Thin	6	18	0	—	0	—	0	—
		Thick	25	19	6	20	1	20	1	20
	Recycled	Thin	2	20	1	20	1	20	0	—
		Thick	0	—	0	—	1	20	1	20
Mill and fill	Virgin	Thin	3	20	2	17	1	20	0	—
		Thick	3	20	2	20	0	—	0	—
	Recycled	Thin	1	20	0	—	0	—	0	—
		Thick	0	—	0	—	0	—	0	—
— Indicates could not be calculated. No. = Number of test sections. Thin = ≤ 2.5 inches (63.5 mm). Thick = > 2.5 inches (63.5 mm).

 

Table 104. Impacts of various treatment types on RFP/RSP of the test sections based on rut depth.

Treatment Type	Mix Type	Thickness	Number of Test Sections and RFP/RSP Values in the Designated Climatic Region
			WF		WNF		DF		DNF
			No.	RFP/RSP (Year)	No.	RFP/RSP (Year)	No.	RFP/RSP (Year)	No.	RFP/RSP (Year)
Overlay	Virgin	Thin	4	20	0	—	0	—	0	—
		Thick	20	20	6	20	0	—	0	—
	Recycled	Thin	0	—	0		1	6	0	—
		Thick	0	—	1	20	0	—	0	—
Mill and fill	Virgin	Thin	3	20	1	20	1	20	0	—
		Thick	3	20	1	20	0	—	0	—
	Recycled	Thin	1	20	0	—	0	—	0	—
		Thick	0	—	0	—	0	—	0	—
— Indicates could not be calculated. No. = Number of test sections. Thin = ≤ 2.5 inches (63.5 mm). Thick = > 2.5 inches (63.5 mm).

 

Table 105. Impacts of various treatment types on RSP of test sections based on alligator cracking.

Treatment Type	Mix Type	Thickness	Number of Test Sections and RSP Values in the Designated Climatic Region
			WF		WNF		DF		DNF
			No.	RSP (Year)	No.	RSP (Year)	No.	RSP (Year)	No.	RSP (Year)
Overlay	Virgin	Thin	2	19	1	11	0	—	0	—
		Thick	13	14	4	12	0	—	1	10
	Recycled	Thin	1	9	1	12	0	—	0	—
		Thick	0	—	1	20	0	—	0	—
Mill and fill	Virgin	Thin	1	20	1	20	1	20	0	—
		Thick	2	12	0	—	0	—	0	—
	Recycled	Thin	0	—	0	—	0	—	0	—
		Thick	0	—	0	—	0	—	0	—
— Indicates could not be calculated. No. = Number of test sections. Thin = ≤ 2.5 inches (63.5 mm). Thick = > 2.5 inches (63.5 mm).

 

Table 106. Impacts of various treatments on pavement performance in terms of RSP based on longitudinal cracking.

Treatment Type	Mix Type	Thickness	Number of Test Sections and RSP Values in the Designated Climatic Region
			WF		WNF		DF		DNF
			No.	RSP (Year)	No.	RSP (Year)	No.	RSP (Year)	No.	RSP (Year)
Overlay	Virgin	Thin	4	6	1	4	0	—	0	—
		Thick	17	8	6	8	0	—	2	10
	Recycled	Thin	0	—	0	—	1	8	0	—
		Thick	0	—	1	10	1	8	0	—
Mill and fill	Virgin	Thin	1	9	1	15	1	8	0	—
		Thick	3	6	2	13	0	—	0	—
	Recycled	Thin	2	5	0	—	0	—	0	—
		Thick	0	—	0	—	0	—	0	—
— Indicates could not be calculated. No. = Number of test sections. Thin = ≤ 2.5 inches (63.5 mm). Thick = > 2.5 inches (63.5 mm).

 

Table 107. Impacts of various treatments on pavement performance in terms of RSP based on transverse cracking.

Treatment Type	Mix Type	Thickness	Number of Test Sections and RSP Values in the Designated Climatic Region
			WF		WNF		DF		DNF
			No.	RSP (Year)	No.	RSP (Year)	No.	RSP (Year)	No.	RSP (Year)
Overlay	Virgin	Thin	4	8	1	6	0	—	0	—
		Thick	16	11	6	17	0	—	1	13
	Recycled	Thin	1	3	1	7	0	—	0	—
		Thick	0	—	1	17	0	—	0	—
Mill and fill	Virgin	Thin	1	11	1	17	1	9	0	—
		Thick	4	16	2	16	0	—	0	—
	Recycled	Thin	2	12	0	—	0	—	0	—
		Thick	0	—	0	—	0	—	0	—
— Indicates could not be calculated. No. = Number of test sections. Thin = ≤ 2.5 inches (63.5 mm). Thick = > 2.5 inches (63.5 mm).

 

IRI

Table 103 lists the average RFPs of test sections located in the same climatic zone and subjected to one of the four treatments listed in the table. The data indicate that the average RFP of the test sections was between 17 and 20 years.

Rut Depth

Table 104 lists the average RFPs/RSPs of test sections located in the same climatic zone and subjected to one of the four treatments listed in the table. The data indicate that except for one test section, the average RFP/RSP of all other sections was 20 years. Again, the exemption was one test section located in the DF region and subjected to thin overlay using recycled AC mixes. Its RFP/RSP was only 6 years. The reason for this RFP/RSP was highly likely problems associated with the AC mix or with construction of the overlay. The AC mix problems could be excessive binder content or unstable mix while the construction issue could be inadequate compaction of the overlay or the early opening of the road to traffic.

Alligator Cracking

Table 105 lists the average RSPs of test sections located in the same climatic zone and subjected to one of the four treatments listed in the table. It is important to note that the labeling as “Alligator Cracking” was highly likely not related to bottom-up fatigue cracks in composite pavements. The label was most likely related to advanced stages of top-down fatigue cracking. Nevertheless, the data in the table indicate that the average RSPs varied from 9 to 20 years detailed as follows:

• In the WF region, the average RSPs of the test sections that were subjected to thin overlay and mill-and-fill treatments using virgin AC mixes were 19 and 20 years, respectively, while the average RSPs of the test sections that were subjected to thick overlay and mill-and-fill treatments using virgin AC mixes were 14 and 12 years, respectively. Further, the RSP of thin overlay treatment using recycled AC mixes was only 9 years.
  
  
• The RSPs of the eight test sections located in the WNF region varied from 11 to 20 years.
  
  
• In the DF region, the RSP of the one test section subjected to thin mill-and-fill treatment using virgin AC mix was 20 years.
  
  
• In the DNF region, the RSP of the one test section subjected to thick overlay treatment using virgin AC mix was 10 years.

Because of the limited number of test sections subjected to a certain treatment and located in one climatic zone, and the lack of time-dependent pavement condition and distress data before treatment, no reliable conclusion could be drawn regarding the benefits of one treatment. For the same reasons the benefits of the various treatments could not be compared.

Longitudinal Cracking

Table 106 lists the average RSPs of test sections located in the same climatic zone and subjected to one of the four treatments listed in the table. The data in the table indicate that the average RSPs varied from 4 to 15 years detailed as follows:

• In the WF region, the average RSPs of the test sections that were subjected to thin overlay and mill-and-fill treatment treatments using virgin AC mixes were 6 and 9 years, respectively, while the average RSPs of the test sections that were subjected to thick overlay and mill-and-fill treatments using virgin AC mixes were 8 and 6 years, respectively. Furthermore, the RSP of thin mill-and-fill treatment using recycled AC mixes was only 5 years.
  
  
• The RSPs of the 11 test sections located in the WNF region varied from 4 to 15 years.
  
  
• In the DF region, the three test sections had an RSP of 8 years.
  
  
• In the DNF region, the average RSP of the test sections subjected to thick overlay treatment using virgin AC mix was 10 years.

Once again, because of the limited number of test sections subjected to a certain treatment and located in one climatic zone, and the lack of time-dependent pavement condition and distress data before treatment, no reliable conclusion could be drawn regarding the benefits of one treatment. For the same reasons, the benefits of the various treatments could not be compared.

Transverse Cracking

Table 107 lists the average RSPs of test sections located in the same climatic region and subjected to one of the four treatments listed in the table. The data in the table indicate that the average RSPs varied from 4 to 17 years, detailed as follows:

• In the WF region, the average RSPs of the test sections that were subjected to thin overlay and mill-and-fill treatments using virgin AC mixes were 8 and 11 years, respectively, while the average RSPs of the test sections that were subjected to thick overlay and mill-and-fill treatments using virgin AC mixes were 11 and 16 years, respectively. Furthermore, the RSPs of thin overlay and mill-and-fill treatment using recycled AC mixes were 3 and 12 years, respectively.
  
  
• The RSPs of the 12 test sections located in the WNF region varied from 6 to 17 years. The thicker the AC overlay was, the longer the RSP was.
  
  
• In the DF region, the one test section had an RSP of 9 years.
  
  
• In the DNF region, the one test section had an RSP of 13 years.

Similar to alligator and longitudinal cracking, because of the limited number of test sections subjected to a certain treatment and located in one climatic zone, and the lack of time-dependent pavement condition and distress data before treatment, no reliable conclusion could be drawn regarding the benefits of one treatment. For the same reasons, the benefits of the various treatments could not be compared.

Summary, Conclusions, and Recommendations for LTPP GPS-7

As noted earlier, the LTPP GPS-7 experiment consisted of the following types of sections:

• Composite pavement test sections that were subjected to AC overlay prior to their assignment to the LTPP Program.
  
  
• JPCP and JRCP test sections that were moved from other LTPP experiments after they were subjected to AC overlay.
  
  
• Composite pavement test sections that were parts of the other LTPP experiments that were milled and filled and moved to GPS-7.

All of the GPS-7 test sections that had more than three after-treatment data points were analyzed and then grouped based on the AC overlay thickness, surface preparation before the AC overlay, overlay type, and climatic regions. It should be noted that the before treatment data were those for rigid pavement, hence they were not included in the comparison of the pavement performance before and after treatment. Nevertheless, results of the analyses are listed in table 103 through table 107. Based on the results of the analyses, the following conclusions were drawn:

• The average RFPs of the test sections in all the climatic regions subjected to any of the treatments previously described was between 17 and 20 years.
  
  
• The average RFP/RSP of all but one test section in all the climatic regions was 20years. The RFP/RSP of that one test section was 6 years, most likely owing to construction problems.
  
  
• Given the limited number of sections available for analyses, no reliable conclusions could be drawn for alligator, transverse, and longitudinal cracking.