Journal of Materials in Civil Engineering

Asphalt has been used as a construction material from the earliest days of civilization, but though it has long been used as a waterproofing material in shipbuilding and hydraulics, its use in roadway construction is much more recent. A recent survey revealed a total of over 2.3 million miles of hard-surfaced (asphalt or concrete) roads in the United States, of which approximately 96% have asphalt surfaces. Asphalt mixture consists of asphalt, coarse and fine aggregate, and a number of additives occasionally used to improve its engineering properties. The purpose of mixture design is to select an optimum asphalt content for a desired aggregate structure to meet prescribed criteria. The demands and reliance upon America’s roadways for mobility and commerce have increased substantially over the past three decades. The highway network is not only the economic backbone of the country, but it also provides the only transportation access to a growing number of communities. This paper presents a review of the past, present, and future trends in asphalt mixture design as the methods have evolved in an attempt to meet the ever-increasing demands of traffic.

The durability of concrete repair may be measured in terms of its resistance to cracking and to ingress by aggressive species. This paper addresses the various issues that form the nucleus of cracking resistance, including the role of material parameter indices such as free drying shrinkage and specific tensile creep. Data for these indices are presented for two new generation repair materials, and attention is drawn to the inherent anomalies existing in international specifications for shrinkage measurement. The paper concludes by defining risk factors associated with the probability of failure of a patch repair in one of three identified modes. The risk factors are computed for a patch repair using a rigid substrate idealization, and the probability of failure in cracking, delamination, or peeling modes is assessed.

The Strategic Highway Research Program (SHRP) fatigue crack initiation life prediction model was based on a sophisticated analysis of the results of intensive bending beam fatigue tests under controlled stress and controlled strain. The definition of crack initiation was defined as the period during which initial microcracks developed into a macrocrack 7.5-mm deep. Due to the lack of the measured crack data, the numbers of loading cycles corresponding to the 7.5-mm deep crack were not observed from the tests but predicted based on a microfracture mechanics model. The objective of this study was to evaluate SHRP fatigue crack initiation life prediction model with the crack measurements in laboratory slab fatigue tests. The study showed that the SHRP crack initiation life model significantly underestimated the fatigue crack initiation life for the slabs. However, the ratio of the observed fatigue life from the slab tests to the crack initiation life predicted from SHRP equation was shown to be approximately constant.

New experimental data make it possible to start with the synthesis of a steel fiber reinforced concrete (SFRC) load resistance model. Four stages are considered: the elastic stage, the stage of closed isolated crack development, and the stages of through-crack development in the absence of fiber ruptures and in their presence. Mathematical expectations of the tensile loads as a function of crack growth or of strains are found. Numerical experiments were carried out. The main results of these experiments were as follows: (1) Longitudinal resistance of fibers to crack growth reaches a maximum, after which it decreases to zero. (2) Transverse resistance increases monotonically. (3) Bond improvement leads to two opposite effects: an increase in longitudinal resistance and an earlier appearance of fiber ruptures. As a result, the total resistance increases if the crack opening is small and decreases if it is large. (4) Increase in the SFRC strength is larger when the bond is better.

Fiber-reinforced polymer (FRP) laminates are being used as external reinforcement for strengthening concrete members. The performance of unidirectional FRP laminates is highly dependent on fiber orientation with respect to applied load direction. In the case of fabrication by manual layup, it is possible to have fiber plies installed with improper orientation. In this project, the degradation of strength and modulus of carbon FRP laminates from fiber misalignment was investigated experimentally using tensile coupons. The specimens consisted of one and two plies of unidirectional carbon FRP impregnated with a two-component epoxy. The misalignment angles varied from 0 to 40° for the one-ply samples, and from 0 to 90° for one ply of the two-ply samples. The size effect on the strength and modulus was investigated for one-ply specimens with misalignments of 5 and 10°. For these specimens, the ply width was maintained constant and the length was varied so that the aspect ratio ranged between 2 and 8. It was concluded that misalignment affects strength more than elastic modulus. However, provided that mechanical parameters are related to the cross-sectional area of laminate with fibers continuous from end to end of the coupon, the degradation of strength can be accounted with a knock-down factor that is independent of misalignment angle.

Chloride diffusion is one of the major causes of deterioration of concrete structures. A large amount of research has been conducted to study the chloride diffusion of concrete, both theoretically and experimentally. Because chloride diffusion experiments are time consuming, it is desired to develop a model to predict the chloride profiles in both steady and unsteady states. This paper studies the feasibility of using a neural network as an adaptive synthesizer as well as a predictor to meet such a requirement. The cascade-correlation algorithm is adopted in the present investigation to predict the chloride profiles diffused through concrete specimens. It is found that the predictions given by the cascade-correlation algorithm are in good agreement with the test results in both steady and unsteady states. The cascade-correlation algorithm can also synthesize an appropriate architecture and train the network simultaneously. It has the potential of becoming an effective tool in the prediction of durability problems. The investigation results demonstrate that the addition of fly ash and microsilica improves the resistance of mixtures to chloride diffusion. However, the addition of calcium nitrite solution degrades the improvement caused by the incorporation of these mineral admixtures, so calcium nitrite should be used in practical engineering with caution.

The porosity of bricks, and their permeability and absorption are very important factors in influencing properties of bricks such as the bond between them and mortar, the resistance of bricks to freezing and thawing, and their chemical stability. This paper suggests new tests for calculating the porosity and water absorption values of clay bricks, which involve the testing of 20-mm brick lumps instead of full brick units.

Cement bypass dust (CBPD) or cement kiln dust is a by-product of the manufacture of portland cement. It is generated during the calcining process in the kiln. Lime (CaO) constitutes more than 60% of CBPD composition. Other compounds include ${\mathrm{SiO}}_2\text{,}$ ${\mathrm{Al}}_2{O}_3\text{,}$ ${\mathrm{Fe}}_2{O}_3\text{,}$ $K_{2}O\text{,}$ ${\mathrm{Na}}_{2}O\text{,}$ ${\mathrm{Cl}}^{-}\text{,}$ etc. Oman Cement Company generates about 25,000–30,000 t of CBPD every year. Some CBPD is recycled back again with the clinker. However, most of the material is disposed of on-site without any further reuse or reclamation. As such, research was carried out to investigate potential reuses of CBPD in the Sultanate of Oman. This paper will present the results of a study that investigated the use of CBPD as a filler in asphalt paving mixtures. Initially, the effect of adding either lime or CBPD (0, 3, 5, 7, 10, and 15%) on binder properties (penetration, ductility, and softening point) was investigated. Then three different asphalt concrete mixtures were prepared using lime (control), and 5 and 13% CBPD substitution for lime or fine aggregate. The mixtures were subjected to Marshall testing. Results indicate that the substitution of 5% CBPD for lime will essentially produce the same optimum asphalt binder content as the control mixture (4.5%, by weight of aggregate) without any negative effect on asphalt concrete properties (stability, flow, voids in total mix, voids in mineral aggregate, and voids filled with asphalt). However, the use of 13% CBPD for lime and fine aggregate will require a higher optimum asphalt binder content of 5.7%, by weight of aggregate. This will produce an uneconomical mix. Thus, 5% CBPD substitution for lime or cement would be the optimum used in asphalt paving mixtures.

This paper describes results from a laboratory investigation into the effects of the interaction between a styrene-butadiene-styrene (SBS) modified bitumen and recycled crumb rubber on the mechanical performance of impact absorbing asphalt (IAA), an asphaltic material that has applications as a sports and safety surface. Curing tests at high temperatures have been undertaken using different rubber-bitumen ratios to assess the amount of bitumen absorbed by the rubber. The changes in bitumen constitution through this interaction have been monitored and related to changes in the rheological characteristics of the residual bitumen. The results show that significant absorption takes place and that the residual bitumen undergoes alterations in terms of its stiffness and viscoelastic balance, together with a reduction in cohesion. A significant finding has been the loss of the polymeric nature of the residual SBS polymer modified bitumen. This has been due to the precipitation of the SBS polymer as the compatibility between the base bitumen and polymer has decreased following the absorption of the lighter, solvating fractions of the binder. To assess the effect of the rubber-bitumen interaction on the mechanical durability of IAA, an abrasive wear test has been developed to simulate the contact between a twisting foot and the surface. This test has been used to compare the mechanical durability of laboratory prepared specimens that have been artificially aged at high temperatures (to simulate the mixing and transportation period before the material is laid and compacted). Results show that there is a detrimental effect on the mechanical durability of the aged material due to the interaction between the rubber and the bitumen.

This research explores the relationship between permeability and crack width in cracked, steel fiber-reinforced concrete. In addition, it inspects the influence of steel fiber reinforcement on concrete permeability. The feedback-controlled splitting tension test (also known as the Brazilian test) is used to induce cracks of up to 500 μm (0.02 in.) in concrete specimens without reinforcement, and with steel fiber reinforcement volumes of both 0.5 and 1%. The cracks relax after induced cracking. The steel fibers decrease the permeability of specimens with relaxed cracks larger than 100 μm.