Journal of Materials in Civil Engineering

This paper describes the results of a six-year laboratory test program to evaluate the performance of chemical-based grouts submerged in a saltwater (brine) environment, simulating a practical application in Saskatchewan, Canada, potash mines. Two types of grout were investigated: (1) Avanti “AV-100 Acrylamide grout;” and (2) Geochem “AC-400 Acrylate grout.” The grouts were prepared underground in a mine at a temperature of approximately 30°C. The specimens were submerged to cure in a nearly saturated NaCl brine solution and transferred to the laboratory for confinement under different pressures of 0, 3.4, and 6.9 MPa (0, 500, and 1,000 psi). The confining pressures were used to simulate different mining conditions and assist in accelerating penetration of brine through the specimens for long-term performance evaluation. Visual inspection and weight loss measurements on each specimen were conducted at ages up to six years. The results of this investigation showed that these chemical grouts deteriorate with time and that this deterioration is dependent on the nature of the grout and on the chemical and the physical environment in which it is placed. The AV-100 grout specimens performed satisfactorily during the first two years of testing. Rapid deterioration associated with large cracks and weight loss up to 82% was observed on specimens subjected to confining pressure of 3.4 and 6.9 MPa during the third to fifth year of testing with no further deterioration in the six years. These specimens shrank to approximately one-fourth of their original volume. In contrast, the AV-100 specimens under atmospheric pressure showed few signs of deterioration after six years of submergence in brine. The AC-400 chemical grout specimens shrank by about 15%–10%, in volume during the first two years of testing. The volume of these grout specimens remained unchanged during the third to the sixth year. However, the AC-400 grout specimens had a total weight loss of 34% during the six years of testing.

Air voids in an asphalt concrete pavement highly influence its performance. Careful consideration of void requirements in compacted bituminous mixtures is more important than stability consideration, since the latter is always higher than necessary. Lack of attention to void requirements may be a direct cause of instability of asphalt concrete pavements. The present work studied the influence of aggregate type and its gradation on the voids in mineral aggregate and air voids of asphalt concrete paving mixtures as compacted according to the Marshall method. Three types of aggregates and five different gradations were employed. Aggregate gradation may be used to control the void requirements in a specific asphalt concrete mixture, influencing and/or affecting other important engineering properties such as water permeability of that specific mixture. On the other hand, aggregate type can provide the necessary voids requirements for an aggregate-asphalt mixture without sacrificing other important engineering properties. Two of the aggregates easily satisfied the void requirements. The third aggregate could not satisfy the same void requirements unless a porous gradation was used. Porous mixtures have more air voids, resulting in an increased permeability to water. This increase in permeability is not the same for different aggregate gradations. The coarser the mix, the higher the rate of increase in the water permeability for the same type of aggregate.

A constitutive model for steel fiber reinforced (SFR) concrete is proposed, in which the tensile behavior incorporates a bilinear strain softening feature. Composite material properties (f_cu, f_t), fiber volume concentration (V_f), fiber aspect ratio (L/d), and fiber-concrete matrix bond stress (τ_d) are used to define the model. The model may also exhibit strain hardening characteristic depending on the magnitude of the variables. Based on the constitutive model, the full history of the flexural moment-curvature relationship for SFR concrete is calculated. Predicted curves are superimposed onto and compared with published experimental data. The results show good overall agreement; the post-cracking softening and post-cracking strengthening response were predicted. In order to facilitate the rapid assessment of the ultimate flexural behavior of SFR concrete, a secondary tensile model is derived from the proposed model. A strain softening parameter (α) is defined for the secondary model and used to evaluate the performance and efficiency of steel fiber reinforcement. The predictive technique using this parameter can be applied to SFR concrete containing various concrete strengths, types of fibers, and fiber concentrations. Charts are presented to assist with fiber selection for flexural design of SFR concrete. Predictions based on the charts are compared with published experimental data.

Flammability tests were conducted on energy-storing wallboard—ordinary gypsum wallboard impregnated with approximately 24% organic phase change material (PCM). Such wallboard is able to store or release a significant amount of thermal energy. The major energy storage factor is the latent heat of the PCM, which is endothermic as PCM melts and exothermic as it crystallizes. A short presentation of the results obtained in the evaluation of such wallboard points out that flammability tests represent almost the last stage in this evaluation. The flammability tests evaluated the surface burning characteristics: flame spread and smoke development classifications determined in a Steiner tunnel, as well as heat and smoke release rates determined by cone calorimeter. The tests indicated that the energy-storing wallboard does not meet all requirements in the National Building Code regarding fire characteristics for building materials. Therefore, the possibility of reducing its flammability is discussed. Comparison of the test results with similar data for other building materials indicates the possibility of reducing the flammability of energy-storing wallboard by the incorporation of a flame retardant.

A quantitative gel fluorescence technique was used to investigate relationships between the extent of alkali silica reactivity (ASR) and properties of concrete cores of varying ages taken from over 20 bridges or pavements in North Carolina. The cores had varying degrees of ASR and were composed of a wide variety of aggregates and cementitious materials. The technique, combining image processing and analysis with a Strategic Highway Research Program qualitative gel fluorescence method, is described and results are discussed. The effects of lamp intensity, thresholding, video averaging, and color based discrimination to differentiate fluorescing areas are reviewed. Preliminary statistical analysis of the technique is presented. While no useful correlation was found between the mechanical properties of cores and the apparent gel content, a strong correlation was found between the percent area of fluorescing material and the log₁₀ expansion of cores after immersion in an alkaline solution for 90 days.

A stochastic-based method of evaluating the interaction parameter (F₁₂) of the Tsai-Wu strength theory has been presented in this paper. Treating all strength parameters of the strength theory as random variables, the mean and standard deviation of F₁₂, under plane stress conditions, have been estimated for Douglas-fir laminated veneer. This estimation has been managed through a nonlinear least-squares fit of the parameters to a cumulative probability distribution of off-axis tensile data. For the purpose of comparison, a sample evaluation of F₁₂ using deterministic methods has been presented. This evaluation showed strong dependence of F₁₂ on angle to grain. A subsequent sensitivity analysis of the off-axis tests on the value of F₁₂ indicated that data from 15° off-axis tensile tests were more stable in establishing F₁₂ than that of other angles tested: 30°, 45°, and 60°.

The creep behavior of metallic materials is frequently studied using creep tests carried out under constant load and constant temperature conditions. This paper presents a general equation that precisely describes the creep-time relationship in such conditions in a succinct format. The equation allows all three classical stages of creep, primary, secondary, and tertiary, to be represented. It expresses creep strain explicitly in terms of real time in a single smooth, continuous curve. It uses six parameters; each independently describes a physical feature of the creep curves. The equation is useful for characterizing experimental results as well as for developing a creep model that can be incorporated into analysis models. Comparison with experimental results shows that the equation closely fits the creep curves of steel at various temperatures and stress levels.

The environmental scanning electron microscope (ESEM) has been used to study water stripping and water penetration in asphalts. ESEM images of an asphalt-coated aggregate showed progressive cracking, flaking, and stripping of asphalt from an aggregate surface as a result of progressive freeze-thaw cycles. ESEM images of an oxidatively aged asphalt that was stored underwater for six and 27 weeks showed evidence of increased water penetration with soak time. The results, although preliminary, demonstrate the feasibility of using the ESEM to study the effects of moisture on asphalts.