Journal of Materials in Civil Engineering

Expansive clay soils—those that change significantly in volume with changes in water content—are the cause of distortions to structures that cost taxpayers several billion dollars annually in the United States. Much has been learned about their behavior over the past 60 years, and relatively successful methods have been developed to modify and stabilize them. This paper reviews some of the key advances developed over the past 60 years in improving our understanding of the nature and methods of modifying and stabilizing expansive clay soils. The state of the practice in stabilization is presented, and practical and research needs to help improve the state of the practice are discussed.

The pseudo-strain concept based on Schapery’s extended nonlinear elastic-viscoelastic correspondence principle is demonstrated by a considerable database to be able to characterize both microdamage and microdamage healing during the damage process. A change in pseudo stiffness can be used to quantify microdamage and healing during the fatigue test. Pseudo stiffness decreases consistently with increasing number of loading cycles, indicating that microdamage occurs during the fatigue test. The significant recovery of pseudo stiffness after rest periods demonstrates a healing effect due to rest periods. Dissipated pseudo-strain energy is a strong and consistent quantifier of damage and healing. High levels of cumulative dissipated pseudo-strain energy are consistent with high levels of fatigue damage, whereas low levels of cumulative pseudo-strain energy are associated with fatigue damage resistance. Pseudo stiffness is the chord slope of the stress-pseudo strain hysteresis loop. Since linear viscoelastic-based time effects are eliminated in this approach, pseudo stiffness and/or pseudo-strain energy are superior indicators of damage than either stiffness or total dissipated strain energy. The effects of rest periods on fatigue life extension due to healing of microcracks are significant. It has been demonstrated that longer rest periods result in more healing, and in turn in greater fatigue life.

One important property of materials is their moisture fixation capacity, i.e., their ability to hold moisture at different relative humidities. The sorption isotherm is one of the main input data in moisture diffusion models, and it can also be used to evaluate properties of the microstructure. We have used four different methods to measure the sorption isotherm of sandstone and porous glass. The first method was to equilibrate samples over saturated salt solutions. The second was a sorption balance in which small material samples were weighed as they were exposed to different relative humidities. The third method was the pressure plate extractor, in which a totally wet sample was equilibrated at various overpressures, corresponding to certain relative humidities. The fourth method was a newly developed microcalorimetric technique to measure sorption isotherms. Despite the different natures of the methods, a satisfying agreement was found.

Sabkha soils are known for their low-bearing strength in their natural condition. Moreover, the collapse potential of sabkhas presents an unacceptable risk in normal practice and calls for the improvement of their mechanical properties prior to any construction. A review of the literature indicates that research on the stabilization of sabkha is scanty despite the extensive distribution of sabkha soils worldwide. Moreover, since the sabkha is a highly variable material, there is a need to formulate a “data bank” by stabilizing as many sabkhas as possible. In this study, a “selected” sabkha soil from Al-Qurayyah, eastern Saudi Arabia, was researched for improving its properties using cement and lime at five different dosages ranging from 0 to 10%. The load-bearing capability of plain and chemically stabilized sabkha mixtures was evaluated using the CBR, unconfined compressive strength, and Clegg impact value at different moisture contents. The results indicated that cement improved the performance of stabilized sabkha much more than lime, particularly at high moisture contents. Further, the 7% cement addition has satisfied the strength requirements so that sabkha soil can be used as a base course in rigid pavements and a subbase in flexible pavements.

Controlled low-strength material (CLSM) is a self-compacting, flowable, low-strength, cementitious material used primarily as backfill, void fill, and utility bedding in lieu of conventional compacted fill. Potential advantages of CLSM include decreased labor requirements, faster construction speed, and potentially lower in-place cost. When considering CLSM as a construction material, two of the most important properties include flowability and compressive strength. The flowability of CLSM can directly impact productivity and human resource requirements for placing the material. Lower flowability may require more resources. In addition, compressive strength values are required as an indicator for performance and long-term excavatability. Minimum strength requirements are necessary for performance criteria, and maximum strength requirements are necessary for long-term excavation. This research investigated the effects of material properties on the water demand necessary to obtain minimum flowability values and a range of compressive strength values for CLSM. Three types of aggregate, three types of fly ash, and one Type I cement were used in this study. A total of 31 mixtures were developed and tested. The use of different aggregate types and sources was found to be the most significant factor affecting water demand in this investigation. Water-cement ratio, aggregate sources, and fly ash type were influencing variables on the compressive strength of CLSM. Formulas were developed to predict the compressive strength development of CLSM for the materials used in this research program.

This paper presents the results of an investigation into the potential application of rubber-modified asphalt in railroad trackbeds by measuring its shear modulus and damping ratio. The measurements of the shear modulus and damping ratio were also conducted on typical subgrade soils. A number of resonant column tests were conducted on subgrade soil samples and the crumb rubber-modified asphalt (CRMA) mix samples with different rubber contents and rubber types. The fine crumb rubber is dissolved in the hot asphalt binder (for a period of time) as an additive to modify the properties of the binder. The measurements were conducted under a wide range of confining pressures and strain levels to simulate stress and strain conditions expected in the typical railway foundation. Cyclic triaxial tests were conducted on subgrade soil samples to study soil characteristics under dynamic loads. It was found that CRMA is a material with high shear stiffness and damping ratio, making it a very attractive material for vibration attenuation of railroad trackbeds.

This paper presents the results of an experimental study undertaken to evaluate the characteristics of the local bond stress-slip response of reinforcing bars (RBs) embedded in plain and steel fiber reinforced concrete (FRC). A total of 32 small-scale beam specimens were tested, through which the influence of the ratio of concrete cover to bar diameter $(c/d_b)$ and the volume fraction of fibers $\left(V_f\right)$ on the response was evaluated. It was found that fiber reinforcement increases substantially the splitting bond strength and leads to a significant improvement in the ductility of bond failure in comparison to plain unconfined concrete. The increases in the local bond strength were 26 and 33% for $V_f$ of 1 and 2%, respectively. Also, increasing $c/d_b$ resulted in a consistent increase in the bond strength, as expected. Compared to the test results of earlier studies, the results of the current investigation clearly demonstrate that pullout specimens largely underestimate the effect of fibers on the bond strength. Based on the results of this study and earlier experimental studies, a model for the local bond stress-slip response of RBs embedded in plain and steel FRC is proposed, and constitutive relationships that describe its characteristic behavior were developed. The relationships are expressed in the functions of the concrete compressive strength $f_c^{\prime }\text{,}$ $c/d_b\text{,}$ and fiber reinforcing index $(V_{f}L/d_f)\text{.}$ The local bond-slip model can be incorporated into a numerical solution scheme of the bond problem to evaluate the influence of different design variables on the development/splice strengths of reinforcing bars embedded in unconfined concrete with or without fiber reinforcement.

This investigation was conducted to assess the efficacy of the Clegg impact hammer (CIH) for estimating the strength of compacted soils by conducting a comparative study between the California-bearing ratio (CBR) and CIH tests. The study was carried out in two phases. In phase 1, compacted marl samples were prepared in the laboratory under three different compactive efforts and different molding moisture contents and then subjected to CBR and CIH tests. Phase 2 focused on conducting in situ CBR and CIH tests on existing soils at some preselected locations as part of ongoing projects in Saudi Arabia. The test results of both phases were statistically analyzed and indicated that the Clegg impact value correlates relatively well with the CBR value for both the laboratory and field tests. These correlations were compared with those reported in the literature. A general, reliable, best-fit model has been proposed for the laboratory, field, and literature data.

This technical note presents the results of compressive, split tensile, and flexural strengths of concrete containing cement kiln dust (CKD) as a replacement for ordinary portland cement (OPC). The replacement levels considered for the study were 20, 40, 60, and 80%. Plain concrete with no CKD was also produced for reference purposes. From the results of the work, it was observed that there was generally a decrease in strength of CKD concrete compared to the reference concrete. However, it was noted that the percentage reduction in strength was minimal when up to 20% of OPC was replaced by CKD in the concrete. The results of the study also confirmed the previous report that the setting time of cement paste increases when CKD is used as a replacement for cement.

Low-density polyethylene (LDPE) has been used by many to modify asphalt cement and to improve the properties of bituminous mixes (hot-mix asphalt). In this investigation, reclaimed polyethylene (PE) obtained from LDPE carry bags was used to modify asphalt cement. The basic properties of modified binder and mixes containing such binders were studied and compared with those of asphalt cement. It was observed that the optimum requirement of PE is 2.5%. Marshall stability, resilient modulus, fatigue life, and moisture susceptibility of mixes were improved as a result of modification of asphalt cement by reclaimed polyethylene.