Scott Shuler

The performance of new asphalt concrete overlays is often jeopardized by existing cracks in the pavement to be rehabilitated. These existing cracks propagate, or reflect, through the new asphalt concrete to the surface of the new overlay. Once reflection cracks appear on the surface of the new pavement, water and debris can enter the pavement structure affecting pavement strength and reducing the life of the overlay. Therefore, reducing the rate at which these reflection cracks propagate to the surface of the pavement is desirable. The research reported in this paper studied the effectiveness of two new reflection crack attenuation techniques. One technique is a grid reinforcing system, the other, a polymer modified asphalt-rich interlayer system. Each system included a control section where no reflective crack attenuation treatment was used. Performance of the two systems was evaluated for six years by measuring cracking semi-annually and comparing this to the cracking present before rehabilitation. After six years significant differences in performance between the controls and the attenuation systems have appeared. Results of this research provide new information regarding tools that may help extend the life of asphalt overlays placed on cracked substrate pavements.

When properly designed, porous asphalt functions both to make safer the driving in wet condition, and to provide hydrologic restoration while functioning as a filtration interface. This study examined the role of aggregate granulometry both on the pore-based indices of porous asphalt and on the clogging resistance. Three groups of porous asphalt gradations comprised of 12 series of samples and separated based on gradation size indices have been examined. For all samples the vertical (k^v) and horizontal (k^h) permeability were measured with the commensurate total void contents (e) and total porosity (n). Also clogging resistance was evaluated by measuring hydraulic conductivity before and after 1 year of exposure of the samples to dust intrusion. Marshall tests were also performed in order to control the stability of the mixes. There was a strong relationship between the permeability and the void content. For a given aggregate gradation, each increment of asphalt content increase caused a decrement in permeability and porosity. As for the clogging resistance potential, it seems to be more related to the initial permeability than to the other pore-based parameters. Results indicated that in addition to the coefficient of uniformity (U) and the total void content, a size-based granulometric index (P₅·P₂·D_max) provided a relationship with vertical permeability and the total void content that were very consistent for the entire range of porous asphalt mixes. Results of this study allow the role of mix design on the permeability to be examined. These mix design results are a necessary precursor to examination of in-situ permeability after placement, and degradation of such permeability as a function of time and rainfall-runoff hydraulic and particulate loadings.

Porous pavements are asphalt or concrete pavement surfaces designed to allow moisture to flow through the surface into an underlying reservoir or into the subgrade soil. Porous pavements prevent pollutants from entering into the water table and therefore, are considered sustainable construction. However, porous pavements eventually fill with debris and get clogged, preventing water infiltration. Thus, the greatest barrier to the use of porous pavements is susceptibility to clogging. Therefore, a major maintenance objective for porous pavements is to prevent clogging of the void spaces within the pavement. This paper describes a potential process of removing particles trapped in the pores of the pavement by flushing water from the bottom to the top of the pavement. Four variables were evaluated in this laboratory experiment to determine effects on particle removal. These were: (1) water pressure; (2) clogging material; (3) pavement porosity; and (4) number of flushes. Results indicate the reverse flush process was effective on both types of clogging material evaluated, was independent of the pavement porosity, and worked for the lowest pressure tested.

Crack sealants prevent moisture and debris intrusion into pavements. The length of time that crack sealants are effective is important to highway agencies. Many highway agencies utilize a magnesium chloride solution to prevent snow and ice accumulation on roadway surfaces. It has been reported that this de-icing solution leaves a residue inside unfilled cracks in asphalt pavements, potentially affecting the performance of crack sealants. The purpose of this study was to assess the effect of magnesium chloride application on the performance of two types of crack sealants at two elevations in Colorado, United States. The experiment was designed to evaluate the association between crack fill remaining over a three year period and two different crack sealants, with and without exposure to magnesium chloride. Using factorial ANOVA, a statistically significant difference (p < 0.05) between the two crack fill products was observed at both elevations; however, the effect of magnesium chloride was only observed for the crack sealants at the higher elevation.

A section of I-25 north of Denver was rehabilitated by cold milling the existing surface to a depth of three in. and replacing with new hot mix asphalt. The contractor received bonuses for quality and smoothness and the mixture passed both Hamburg and French LCPC rut tests. Within 1 year longitudinal cracks appeared in the pavement surface. The cracking appeared in the driving lanes of both the north and southbound directions. The severity of the cracking ranged from low to high. An investigation concluded that cracking on the project was surface initiated and caused by a number of factors. One factor was segregation observed at the bottom of the upper pavement lift that was not visible on the surface. After this so-called “top-down cracking” was discovered on this first project, other pavements began manifesting similar traits. Therefore, a statewide evaluation was conducted to determine the extent of this distress in other pavements. As a result of this study 28 sites were evaluated and of these 18 contained top-down cracking. Based on this finding a change in the mixture design process was implemented to allow for increased asphalt content in hope that the richer mixtures would not be as prone to segregate. In addition, a segregation task force was created with industry to develop a specification for segregation. This task force is in the process of developing a specification to identify subsurface segregation with the elimination of top-down cracking as the goal. Paving equipment manufacturers have also identified areas within the laydown equipment that can promote segregation. As a result manufacturers have taken the initiative to develop an antisegregation retrofit for some laydown machines. As a result of these efforts top-down cracking has been generally eliminated or, at least, greatly reduced.

Longitudinal edge cracking has caused asphalt pavement failure in Colorado for many years. The purpose of this research was to determine the probable cause or causes of edge cracking in asphalt pavements in residential subdivisions. Eight locations at three sites in Colorado were sampled. A fourth site was identified, and soil samples were collected before construction in an attempt to obtain precracking soils data. The three primary findings of the study were 1). The edge cracking observed at all eight locations in this study began at the top of the pavement. This means that upward movement from below and/or bending is causing excessive tensile strain at the surface of the pavement. 2) Lower density and higher moisture than optimum of the subgrade beneath the edge cracks appears to be related to the cracking. 3) The soils at all locations were plastic clays with potential for high volume change. It seems likely that swelling of these soils contributed to the edge cracking; however, no strong correlation was found.

Capital equipment acquisition is an important process in the heavy construction industry. Equipment is often one of the largest investments for a company and has a significant effect on cash flow and profit potential. The purpose of this article is to investigate capital equipment acquisition processes of heavy construction companies. The equipment acquisition process was analyzed by evaluating equipment replacement policies, the position of the individual making equipment purchasing decisions, and the effect of company size on equipment replacement policy. A questionnaire was used to survey members of the Associated General Contractors of America and various asphalt and concrete pavement trade associations in the United States. Results suggest there is a direct correlation between the size of the company and the use of capital budgets and equipment policies as decision-making tools. Results further indicate that the chief executive officer is often the decision maker when it comes to equipment acquisition, regardless of company size. Equipment replacement is based on repair cost and equipment efficiency. An average of 75% of equipment is owned and is paid for in cash or through lease-buy options.