Journal of Materials in Civil Engineering

Expansion and cracking of portland cement concrete containing glass aggregates have been known for decades. Traditional alkali-silica reaction and expansion mechanisms are being used to explain the reaction and expansion mechanisms of cement concrete containing glass aggregates. This paper reviews glass chemistry, alkali-silica reaction mechanism, expansion of concrete containing glass aggregates, and microstructure of the interfacial transitional zone between cement paste and glass particles. Analysis of these published results indicates that the formation of expansive sodium-calcium silicate hydrate (N-C-S-H) gel around glass particles in concrete results from the dissolution and precipitation of soda-lime glass in high pH environments and not from the reaction between glass particles and the alkalis in cement. The corrosion of soda-lime glass and formation of N-C-S-H can happen when the pH of the pore solution is greater than 12 regardless of the presence of alkali ions. Thus, the expansion of concrete containing glass aggregates is different from that caused by traditional alkali-silica reaction. The presence of moisture and high pH $\left(>12\right)$ are the two necessary conditions for concrete containing glass aggregates to expand.

Soil-cement blocks are employed for load bearing masonry buildings. This paper deals with the study on the influence of bed joint thickness and elastic properties of the soil-cement blocks, and the mortar on the strength and behavior of soil-cement block masonry prisms. Influence of joint thickness on compressive strength has been examined through an experimental program. The nature of stresses developed and their distribution, in the block and the mortar of the soil-cement block masonry prism under compression, has been analyzed by an elastic analysis using FEM. Influence of various parameters like joint thickness, ratio of block to mortar modulus, and Poisson’s ratio of the block and the mortar are considered in FEM analysis. Some of the major conclusions of the study are: (1) masonry compressive strength is sensitive to the ratio of modulus of block to that of the mortar $\left(E_b/E_m\right)$ and masonry compressive strength decreases as the mortar joint thickness is increased for the case where the ratio of block to mortar modulus is more than 1; (2) the lateral tensile stresses developed in the masonry unit are sensitive to the $E_b/E_m$ ratio and the Poisson’s ratio of mortar and the masonry unit; and (3) lateral stresses developed in the masonry unit are more sensitive to the Poisson’s ratio of the mortar than the Poisson’s ratio of the masonry unit.

The results of an experimental study conducted on specimens similar to ASTM G109 made with different types of cement and steel, and varying water/cement (w/c) ratios are reported in this paper. A portion of the top surface of the specimens was subjected to an exposure to 3% sodium chloride solution followed by an exposure to air, in cycles, for a large number of repetitions. Half-cell potential measurements were carried out periodically at the beginning of every exposure to chloride solution and also just prior to exposure to air, until a sudden drop in the potential was noticed. The average half-cell potential value of top steel bar, after sudden drop, is observed to be nearly the same, irrespective of steel, cement, and w/c ratio. However, corresponding free and total chloride concentrations, just after the preceding sudden drop, varied with experimental factors. The aforementioned sudden drop is also accompanied by reversal in the direction of current between top and bottom steel bars, indicated by a sign change in the potential difference. Thus, it is demonstrated that half-cell potential is a stable indicator of rebar corrosion initiation.

The detrimental impact of the intrusion of moisture into base and subgrade layers of pavements is well quantified based on laboratory tests, and is documented in a number of field studies. Due to construction variability and limitations of the instrumentation and test devices, the field trends contain some scatter. A series of well-controlled tests was carried out on small-scale specimens (1 m in diameter) to determine the feasibility of quantifying the impact of moisture on one base and two types of subgrade. To achieve this goal, a test setup was designed and used. To determine how realistic the outcome from these experiments was, the results were compared with those from two full-scale test sections made from the same materials. The results from the small-scale and full-scale tests were also compared with the outcomes of numerical models. The experimental results from the small-scale and full-scale tests were quite similar. The trends from the numerical models were also similar to the experimental results; however, a transfer function was needed to match the two. Based on this study, the small-scale tests can lead to similar outcomes much faster and with enormously less cost in comparison to full-scale field tests.

The focus of this work was to evaluate the use of commercially available matting systems to sustain C-130 and C-17 transport aircraft loads over soil bases having different California bearing ratio (CBR) ranges. Test sections were constructed using three range of CBR: high $\left(\text{CBR}=40–50\right)$ , medium $\left(\text{CBR}=8–10\right)$ , and low $\left(\text{CBR}=5–6\right)$ . Testing began with the C-130 load cart and six different matting systems. The C-130 was the lesser of the two aircraft loads examined and this initial testing was used as an “elimination round” for the various matting systems chosen. Matting systems deemed suitable for the C-130 were further tested under the C-17 load cart. Systems were evaluated based on logistical and assembly requirements, mat damage sustained during traffic, and accumulated deformation of the mats and soil during traffic. The latter are shown in line plots of passes versus plastic rut formation. Summary information on each matting system tested and the test sections themselves is presented. Conclusions on the matting systems tested and their application are discussed.

A split Hopkinson pressure bar equipment was used to perform high strain rate compressive tests on concrete filled steel tubes (CFT) along with benchmark plain concrete cylinders for comparison. This paper reports the results of dynamic compressive strength, ultimate strain, residual strength and the secant stiffness. The dynamic increase factor (DIF) of CFT strength upon the increase of strain rate was obtained based on the logarithm linear fitting of the test results. The DIF of the CFT specimens can be relatively well estimated with conservatism using the simple superposition of dynamic uniaxial strength of concrete and steel. The confinement stress and the confinement coefficient under high strain rate loading are also discussed based on assumptions similar to those used for the static loading cases.

Earlier studies have established that aggregates could be produced from fly ash through pelletization, which has the advantages of reducing (1) environmental pollution and (2) consumption of depleting natural aggregates. Though cement, lime, and bentonite were used for improving the properties of fly ash aggregates, limited studies have been reported on the effect of binders on the pelletization process of fly ash. This paper discusses the relative performance of bentonite with two different swelling characteristics on the pelletization of fly ash. The variation of factors and its optimum level on the overall pelletization efficiency, efficiency of producing three individual size fractions, ten percent fines value, and water absorption were determined through a statistically designed experiment using response surface methodology. The maximum pelletization efficiency of fly ash aggregate was achieved with lower dosage level of high swelling bentonite. Higher factor levels facilitate enhanced ball growth, i.e., produce aggregate size fraction greater than 10 mm. Similarly, the maximum ten percent fines value and minimum water absorption result at the maximum level of the factors studied. The optimal level of factors for a given aggregate size fraction was almost similar, independent of swelling characteristics of bentonite, except for the variation in bentonite and moisture contents.

This study presents a self-consolidating concrete mix developed for thin wall construction. Casting of vertical thin concrete walls requires a stable, pumpable, and highly flowable mix. The developed mix has increased fine-to-coarse aggregate ratio, 20% fly ash replacement, a low $w/cm$ ratio, a superplasticizer, an accelerator (optional), and a viscosity modifying admixture. A special placement method was designed for pumping the concrete from the bottom of the vertical wall form. Concrete walls of 75-mm thickness reinforced with one or two steel grid layers were cast and loaded to failure under one-way and two-way bending configurations. The one-way slabs resembled portal frames and were loaded with a line load along the centerline. Plastic hinges formed at the centerline of the one-way slabs and then at a corner, where reinforcement was greater. The two-way slabs were loaded with a small-area concentric uniform distributed load. A yield line strength analysis was performed and matched quite closely the experimental capacities. It was concluded that it is possible to cast high strength vertical thin walls with self-consolidating concrete by pumping from the bottom of the form.

The results of the dynamic pressurization test and of the radial flow-through test on hollow cylinders of the same material are compared to validate the newly developed hollow dynamic pressurization technique. The results from testing Vycor glass and cement paste indicate close agreement between the two test methods, which supports the validation of the hollow dynamic pressurization test as an accurate and repeatable method for measuring the permeability of porous materials. The results also provide an interesting and original comparison between a new poromechanical technique and a more traditional flow-through technique. Additionally, the permeability values from this study agree reasonably well with values presented in the recent literature.

New method of mixture proportioning is proposed for concrete made with coarse recycled concrete aggregates (RCA). The proposed method, dubbed the “equivalent mortar volume” method, is predicated on the fact that RCA is a two-phase material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture involving RCA, one must account for the quantity and quality of each phase and adjust both the coarse aggregate and fresh paste content of the mix accordingly to achieve the same total mortar volume as a companion mix with the same specified properties but made entirely with coarse natural aggregates of similar properties to the coarse natural aggregate contained in RCA. Using the proposed method and the conventional aggregate replacement method, a large number of mixes was made with RCA obtained from two demolition waste recycling plants. For each mix, its slump, fresh and hardened densities, compressive strength, and elastic moduli were measured. The results showed that using the proposed method, unlike the conventional method, yields concrete mixes with consistent, predictable, and comparable properties to those of similar mixes made with natural aggregates.

An asphalt mixture generally behaves as an insulator. The addition of electrically conductive additives may produce conductive asphalt mixtures. The present study investigated the effectiveness of several commonly used conductive additives to produce electrically conductive hot-mix asphalt (HMA). The effects of three conductive additives, a micron-scale steel fiber, a carbon fiber, and graphite, on some laboratory-measured properties of HMA mixtures were investigated through mixture performance testing. The results from this study indicated that the micron-scale steel fiber was the most effective additive to produce conductive HMA. The inclusion of steel and carbon fibers improved permanent deformation properties, maintained the indirect tensile cracking resistance, and slightly reduced the dynamic modulus of the conductive HMA. The inclusion of graphite as an electrically conductive additive significantly improved the rut resistance, increased the dynamic modulus, and significantly reduced the indirect tensile cracking resistance of the conductive HMA mixtures.

The main objective of this research is to investigate the potential use of pyrolisis low density polyethylene (LDPE) as a modifier in hot mix asphalt paving mixtures. Five different blends including conventional mix were subjected to binder testing such as rheological tests, as well as to some other tests related to the homogeneity of the system. Optimum asphalt content was obtained by Marshall method and used in all the modified mixes. The engineering properties, including Marshall stability, indirect tensile strength, and compressive strength were determined. Research results indicate that modified binders showed higher softening point, keeping the values of ductility at minimum range of specification of $\left({100}^{+}\text{cm}\right)$ , and caused a reduction in percentage loss of weight due to heat and air (i.e., increase durability of original asphalt). The results indicated that the inclusion of pyrolisis LDPE with asphalt concrete mixtures gave a quite satisfactory result in terms of stability and other Marshall properties, increase in indirect tensile, and compressive strength.