Journal of Materials in Civil Engineering

A case history is presented of a no‐fines concrete subgrade slab through which soft waters had been percolating for several years. The slab was intended to act as a drainage layer, but elements of the drainage system became blocked due to calcium‐based deposits after a relatively short period in service. The paper presents the results of water and solid‐deposit analyses that were carried out, and discusses the mechanism of deposition and blockage of the drainage system. The rates of dissolution of the slab and the potential for continued blockage of the drainage pipes are also examined. Remedial measures based on these assessments were adopted. The case serves as a useful example of the importance of proper understanding of materials technology in civil engineering construction.

Steel‐fiber concrete (SFC) demonstrates better deformational and cracking characteristics as compared to plain concrete and is used in structures where significant tensile stresses are encountered. Also, recent experimental studies have indicated that an improvement in the biaxial compressive strength of plain concrete can be achieved by the addition of steel fibers. In this paper, an attempt is made to obtain analytically the failure envelope for the steel‐fiber concrete under biaxial compression. In this approach, the biaxial compressive behavior of steel‐fiber concrete is modeled as that of ordinary concrete under triaxial compression, with the stress in the third direction taken equal to the confining pressure due to fibers. Thus the failure envelopes are obtained by using the material laws for fiber concrete and a suitable model for the plain concrete under triaxial compression. The predictions of the analytical model are found to compare well with the available experimental results.

This paper presents an experimental analysis of the relationship between the relative quantity of a particular‐size molecule in asphalt cement and the mechanical properties of asphalt concrete. Three AC‐20 grade asphalt cements (AC) and recovered asphalt cements from four sources were used for high pressure‐gel permeation chromatography (HP‐GPC) testing and for preparing asphalt‐concrete mixtures. Specimens of laboratory‐prepared asphalt concrete and field cores were tested for tensile strength and resilient modulus in dry and wet conditions. Multiple‐regression analyses indicate that tensile strength and resilient modulus had significant correlations with certain areas of chromatograms that are divided into 10 slices. Tensile strength appears to be sensitive to variation of the relative areas of the second and third slices $(T_2+T_3)$ and resilient modulus vary with the area of the first, second, and third slices $(T_1+T_2+T_3)$. In general, higher relative quantity of larger size molecules cause lower tensile strength and resilient modulus. However, there was no threshold value of the relative quantity of large molecules that showed a peak value for a mechanical property.

Polymer concrete (PC) has been widely used for floor and bridge overlays, but because of the differences in the coefficients of thermal expansion between Portland‐cement concrete (PCC) and PC, there is concern about possible delamination at the interface. This paper is a report of the results of two experimental studies. The first was an investigation of crack propagation, stiffness deterioration, and delamination of PC‐PCC composite members subjected to load cycles at room temperature. The second was an investigation of the interface shear stresses and longitudinal normal stresses of PC‐PCC beams under various uniform thermal loads ranging from approximately 3°F (16°C) to 140°F (60°C). A hypothesis of the thermal phase was that interface shear stresses are localized near the ends of the beams. It was observed that: (1) Test beams survived 2,000,000 load cycles without delamination and without significant loss of stiffness; (2) interface shear stresses are end bound; and (3) the effective length of the end zone in which shear stresses are concentrated is approximately equal to the depth of the composite member.

Accumulations of worn‐out automobile tires create fire and health hazards. As a possible solution to the problem of scrap‐tire disposal, an experimental study was conducted to examine the potential of using tire chips and crumb rubber as aggregate in portland‐cement concrete. This paper examines strength and toughness properties of concrete in which different amounts of rubber‐tire particles of several sizes were used as aggregate. The concrete mixtures exhibited lower compressive and splitting‐tensile strength than did normal concrete. However, these mixtures did not demonstrate brittle failure, but rather a ductile, plastic failure, and had the ability to absorb a large amount of plastic energy under compressive and tensile loads. A mathematical model is used to describe the effects of rubber aggregate on the compressive and tensile strength reduction of concrete.

Current adhesion theories fail to explain completely the stripping phenomenon. Quantification of stripping potential prior to mix design, and based on variables described in current adhesion theories, remains difficult. Current laboratory evaluation procedures are not completely reliable and fail to predict, with accuracy, the stripping susceptibility of various asphalt concrete mixes. This paper evaluates the existing adhesion theories and stripping mechanisms suggested in the literature. Factors contributing to the lack of success in predicting stripping susceptibility of asphalt concrete in the laboratory are also discussed. An earlier comprehensive investigation of the stripping phenomenon revealed serious deficiencies in the current approach to the problem. First, the interaction between the different components of the asphalt‐concrete mixture under a wide temperature range is neglected. It is proven that differential thermal contraction, as a result of the large difference in the coefficients of thermal contraction, is an important factor. This paper addresses another deficiency, which is the lack of a precise description of the location where debonding associated with moisture occurs. Observations made during the experimental investigation revealed that initial separation in the compacted mix takes place between the asphalt matrix (mix of asphalt cement and fine material) and coated aggregate particles.

Stripping has damaged some of South Carolina's asphaltic concrete pavements. It is not known whether the material properties of stripped asphalt pavement will allow its use for recycling. A field and laboratory study was initiated to investigate the feasibility of reusing moisture‐damaged asphaltic concrete; to determine the effects of antistrip additives on recycled mixtures; and to evaluate the recycled mix design procedures that use cored reclaimed asphalt pavement (RAP) instead of milled RAP. A total of 144 laboratory Marshall specimens were made and tested. In addition, field cores were obtained and tested before and after recycling. The dry and wet modulus resilience (MR) and indirect tensile strength (ITS), visual strip rating (VSR), and air voids (AV) of all specimens were obtained. Marshall specimens containing moisture‐damaged asphaltic concrete mixtures produced significantly higher strength values than those using only virgin material. Antistrip agents were found to be effective in increasing the strength of specimens in the saturated condition. The results also showed no significant differences among strengths of samples prepared with cored and milled RAP.

An experimental program consisting of resilient modulus and creep‐rebound testing was conducted to determine the effects of aggregate top size on the stiffness and resistance to permanent deformation of bituminous concrete mixtures. Three aggregates (two pit‐run alluvial deposits and one crushed limestone) were investigated at three top sizes (19.1 mm, 25.4 mm, and 31.8 mm). Stiffness and resistance to permanent deformation were found to decrease with increasing top size when alluvial aggregates were used and to increase when crushed limestone was used. This is attributed to the percentage of fractured faces that occur near the top size of the aggregate's gradation. For the alluvial aggregates, the percentage of fractured faces decreased with increasing aggregate top size. For the crushed limestone, the percentage of fractured faces was essentially 100% for all top sizes studied.