W Spencer Guthrie

Effects of Reclaimed Asphalt Pavement on Mechanical Properties of Base Materials

The purpose of this research was to investigate the influence of reclaimed asphalt pavement (RAP) on the mechanical properties of recycled base materials typical of northern Utah. Two sources of RAP, two sources of base, and five RAP contents were evaluated in a full-factorial experimental design in which the California bearing ratio (CBR) test, free–free resonant column test, and tube suction test were used to measure strength, stiffness, and moisture susceptibility, respectively. A fixed-effects analysis of variance was performed on the collected data. The results indicate that, on average, CBR values decrease between 13% and 29% with each 25% increase in RAP. For stiffness testing at the optimum moisture content determined for each blend, the general trend was a decrease in stiffness from 0 to 25% RAP, followed by a steady increase in stiffness as the RAP content was increased from 25% to 100%. Following a 72-h oven-drying period, however, the general trend reversed; an increase in stiffness occurred as the RAP content was increased from 0 to 25%, and a decrease in stiffness was observed for RAP contents above 25%. For the moisture-susceptible base material tested in this study, additions of 25% and 50% RAP actually increased the moisture susceptibility of the recycled material compared with the neat base, although the blended material was classified as non-moisture-susceptible when the RAP content was 75% or higher. Base stabilization may be required in many instances to ensure adequate strength and durability of recycled materials.

Cement Stabilization of Aggregate Base Material Blended with Reclaimed Asphalt Pavement

The effects of reclaimed asphalt pavement (RAP) content and cement content on the strength and durability of recycled aggregate base materials typical of the I-84 pavement reconstruction project performed in Weber Canyon near Morgan, Utah, were investigated. The laboratory work was based on a full-factorial experimental design, including five RAP contents, five cement contents, and three replicate specimens of each possible treatment. Measurements of unconfined compressive strength (UCS) and final dielectric value in the tube suction test (TST) were used to assess material strength and durability, respectively. These data, together with dry density measurements, were evaluated through an analysis of variance (ANOVA). The results of the ANOVA performed on the UCS data indicate that UCS decreases from 425 to 208 psi as RAP content increases from 0% to 100% and increases from 63 to 564 psi as cement content increases from 0.0% to 2.0%. Similarly, the final dielectric value decreases from 14.9 to 6.1 as RAP content increases from 0% to 100% and decreases from 14.0 to 5.8 as cement content increases from 0.0% to 2.0%. Increasing RAP contents generally correspond to decreasing dry densities. With design criteria requiring 7-day UCS values between 300 and 400 psi and final dielectric values less than 10 in the TST, the results of this research suggest the use of RAP contents in the range of 50% to 75% and a cement content of 1.0% for this material.

Early-Age Strength Assessment of Cement-Treated Base Material

To avoid early-age damage to cement-treated base (CTB) materials, the cement must be allowed to cure before the pavement can be opened to traffic. The purpose of this research was to evaluate the utilities of the soil stiffness gauge (SSG), the heavy Clegg impact soil tester (CIST), the dynamic cone penetrometer, and the falling weight deflectometer for assessing early-age strength gain of cement-stabilized materials. Experiments were performed at four sites on a pavement reconstruction project along I-84 in Morgan, Utah, where cement stabilization was used in conjunction with full-depth recycling. Each site was stationed to facilitate repeated measurements at the same locations with different devices and at different curing times. Because of the considerable attention from the pavement construction industry for routine quality control and quality assurance programs, the SSG and CIST were the primary focus of the research. Statistical techniques were used to evaluate the repeatability of these devices and...

Frost Heave and Water Uptake Relations in Variably Saturated Aggregate Base Materials

The occurrence of frost heave in soils and aggregates can be attributed to the redistribution of water in the soil profile. Frost heave testing performed in this study on 71 variably saturated specimens of aggregate base material indicates that although the uptake of new water from outside the soil body is a primary source of moisture in the formation of segregation ice, internal water residing within the soil or aggregate structure can serve as an important supply of water to the freezing front. Frost heave concepts relating to unsaturated soil conditions were reviewed, and a laboratory methodology was employed to study the relationships between the physical properties of the specimens and their frost heave behavior. Degrees of saturation ranging from 45% to 84% were evaluated, and heave–uptake ratios as high as 2.24 were calculated. Ratios less than 1.09 suggest that sufficient porosity exists in the sample matrix to allow the formation of ice without causing frost heave; higher ratios designate samples that are nearly saturated and that undergo substantial upward redistributions of existing water during the initial freezing process, which gives rise to measurable heave even before additional water is imbibed by the sample. The entry of air into freezing soils and aggregates can play an important role in their frost heave behavior.

Laboratory Characterization of Recycled Concrete for Use as Pavement Base Material

The purpose of this research was to characterize both demolition and haul-back sources of recycled concrete material (RCM) available in Utah County, Utah, for use as pavement base material and to investigate the self-cementing behaviors of each. A telephone survey was conducted to assess the state of the practice with respect to the local use of RCM, and extensive laboratory testing was performed to evaluate the strength and durability properties of both sources of RCM. Laboratory testing included determinations of particle-size distributions, Atterberg limits, specific gravity values, absorption characteristics, moisture-density relationships, California bearing ratio (CBR), unconfined compressive strength (UCS), stiffness, resistance to freeze-thaw cycling, tube suction test (TST) moisture susceptibility classifications, and Los Angeles abrasion losses. The results of the testing indicate that marked stiffening and strength gain of the materials occur within a 7-day curing period, although the rate and ...

Effects of Initial Surface Treatment Timing on Chloride Concentrations in Concrete Bridge Decks

In consideration of concrete cover thickness and the presence of stay-in-place metal forms (SIPMFs), research was done to determine the latest timing of initial surface treatment applications on concrete bridge decks subjected to external chloride loading before chlorides accumulate in sufficient quantities to initiate corrosion of the reinforcing steel. Chloride concentration data for this research were collected from 12 concrete bridge decks located within the Interstate 215 corridor in Salt Lake City, Utah. Numerical modeling was used to generate a chloride loading function and to determine the diffusion coefficient of each deck. On the basis of average diffusion coefficients for decks with and without SIPMFs, chloride concentration profiles were computed through time for cover thicknesses of 2.0 in. (50.8 mm), 2.5 in. (63.5 mm), and 3.0 in. (76.2 mm). The results of the work show that the average diffusion coefficient for bridge decks with SIPMFs is approximately twice that of decks without SIPMFs and that, on average, each additional 0.5 in. (12.7 mm) of cover beyond 2.0 in. allows an extra 2 years for decks with SIPMFs and 5 years for decks without SIPMFs before a surface treatment must be placed to prevent excessive accumulation of chlorides. Although the data generated in this research are based on conditions typical of bridge decks in Utah, they clearly illustrate the effect of cover depth and the presence of SIPMFs. This information may be especially valuable to bridge engineers and managers responsible for programming surface treatments on concrete bridge decks.

Effects of Soil Clogging and Water Saturation on Freeze-Thaw Durability of Pervious Concrete

The objective of this research was to evaluate the resistance of pervious concrete to degradation during freeze–thaw cycling under different soil clogging and water saturation conditions. Laboratory testing of freeze–thaw durability involved two levels of soil clogging and two water saturation conditions in a full-factorial experimental design, and field testing involved measurements of stiffness and compressive strength on clogged and unclogged locations of an experimental pervious concrete slab placed in northern Utah. Both experimental factors, together with their interaction, were determined to be statistically significant in this research. Specimens that were clogged with soil or completely submerged in water, or both, were damaged at a significantly faster rate than those specimens that remained unclogged and unsaturated. The average number of freeze–thaw cycles to failure was 93 for clogged specimens compared with 180 for unclogged specimens, and 80 for saturated specimens compared with 193 for unsaturated specimens. A comparison of in situ modulus values, core modulus values, and core compressive strengths associated with clogged locations and unclogged locations in the experimental slab indicated no significant differences in structural properties in the clogged and unclogged locations. That was likely attributable to the fact that only the upper 1 to 2 in. of pervious concrete in clogged locations was filled with debris. The remaining depth of the slab seemed to be free draining. These research findings emphasize the importance of ensuring that pervious concrete remains free of debris and well drained during service in cold regions.

Effects of Environmental Factors on Construction of Soil-Cement Pavement Layers

The specific objectives of this research were to quantify the effects of certain environmental factors on the relative strength loss of soil–cement subjected to compaction delay and to develop a numerical tool that can be easily used by engineers and contractors for determining a maximum compaction delay time for a given project. These objectives were addressed through extensive laboratory work and statistical analyses. The laboratory work involved testing an aggregate base material and a subgrade soil, each treated with two levels of cement. Environmental factors included in the experimentation were wind speed, air temperature, and relative humidity; three levels of each factor were evaluated in combination with three compaction delay times. The primary response variables in this research were relative compaction and relative strength. The findings indicate that relative strength is sensitive to variability among the selected independent variables within the ranges investigated in this research, while relative compaction is not. Inferring relative strength from relative density is therefore not a reliable approach on soil–cement projects. Consistent with theory, higher wind speed, higher air temperature, lower relative humidity, and higher compaction delay time generally result in lower relative strength. With the nomographs developed in this research, the maximum delay time permitted for compaction of either a base or subgrade material similar to those tested in this research can be calculated. Knowing in advance how much time is available for working the soil–cement will help contractors schedule their activities more appropriately and ultimately produce higher-quality roads.

Variability in Construction of Cement-Treated Base Layers: Material Properties and Contractor Performance

Construction factors most correlated to specific mechanical properties of cement-treated base (CTB) layers were identified. Construction factors that exhibit comparatively high variability within individual construction sections of the two pavement reconstruction projects included in this study were determined. In addition, differences between construction sections tested in this research were evaluated. Researchers collected extensive field and laboratory data, which were analyzed using several statistical techniques. The results of this analysis suggest that reduced spatial variability is needed in reclaimed asphalt pavement (RAP) content, cement content, and time between mixing and compaction, which were all identified as important predictors of CTB strength in this study. For full-depth reclamation projects, milling plans should be used to achieve improved uniformity in RAP content, and inspection protocols for encouraging improved control of cement content during construction should be implemented to ensure high-quality work. Compaction should be performed as soon as possible after mixing to minimize the adverse effects of cement hydration on the ability to achieve maximum dry density in the field. Minimizing variability in construction of CTB layers will ultimately lead to higher-quality pavements that more consistently meet design expectations.

Effect of stay-in-place metal forms on performance of concrete bridge decks

The primary objective of this research was to investigate the effect of stay-in-place metal forms (SIPMFs) on corrosion of steel reinforcement in concrete bridge decks. The study included 12 concrete bridge decks located within the Interstate 215 corridor in the vicinity of Salt Lake City, Utah. All decks were subject to similar traffic loading, climatic conditions, and maintenance treatments, including applications of deicing salts during winter months, and had been constructed during 1984-1989 with epoxy-coated rebar. Test methods included visual inspection, chain dragging, hammer sounding, Schmidt hammer testing, half-cell potential testing, and chloride-concentration testing. An analysis of covariance (ANOCOVA) was performed to evaluate the effect of SIPMFs on each of the 13 deck properties measured. Five of the 13 analyses yielded significant results, including age, cover, Schmidt rebound number, half-cell potential, and chloride concentration at 2-in. depth. While differences in age and cover result...