Journal of Materials in Civil Engineering

Accelerated corrosion tests were carried out on reinforced‐concrete specimens made with plain and 10% and 20% microsilica‐blended cements. Time to corrosion initiation and corrosion rates of reinforcing steel were measured. Pore fluid was also extracted for analysis from chloride‐bearing hardened cement pastes. Results show that in terms of corrosion‐initiation time, microsilica‐blended cement concretes perform threefold better than the plain cement concrete. After the initiation of corrosion, reinforcing steel in microsilica‐blended cement concrete shows no significant reduction in corrosion rates. Partial cement replacement by microsilica, sharply increases the Cl⁻/OH⁻ ratio of the pore solution. In addition to the adverse changes in the chemical environment, microsilica blending also brings about significant improvements in the pore structure of the cementitious matrix. The higher corrosion‐initiation time of the microsilica‐blended cement concretes is ascribable to observed pore refinement and segmentation, which retards the diffusion of chloride ions to the steel‐concrete interface, thereby delaying the onset of corrosion. Data developed in this study show microsilica‐blended cement concrete will provide significantly more protection to steel when secondary chlorides permeate into concrete from external sources during service life, compared to situations where primary chlorides are introduced during mixing.

In the companion paper, expressions were derived for the protected paste volume of air‐entrained cement paste on the basis of hydraulic pressure theory. The protected paste volume is the common volume of cement paste protected from frost damage by all the various‐sized air voids in the paste. The expressions derived earlier assumed that the user had knowledge of the complete air‐void distribution in concrete. In this paper, the expressions derived earlier are converted to forms using readily available linear traverse data. The derivations are validated using computer simulations. It is shown that the paste parameter that appears in the expressions can be estimated using a few material properties of cement paste. The calculation of the protected paste volume is illustrated for a concrete sample tested in the laboratory. The protected paste volumes of a variety of concretes tested in two other laboratories are then calculated and correlated with their frost resistance. It is shown that the protected paste volumes of the concretes analyzed correlate well with their frost resistance.

Three epoxy mortar materials are subjected to failure tests in compression and split‐cylinder tension over a temperature range of −35°–200°F. The tests are completed using 76.22‐mm‐ (3‐in.) diameter, 152.4‐mm‐ (6‐in.‐)long cylinders and failed specimens are examined using a microscope. Axial and radial strains are measured during the compressive tests to determine the compressive modulus and Poisson's ratio. All three mortar materials exhibit an apparent linear relationship between ultimate compressive strength and temperature. The split‐cylinder tensile test results show that tensile strength varies linearly with temperature at temperatures below the glass transition region. The compressive modulus is found to increase with decreasing temperatures. The mode of failure also varies with temperature, and microscopic examination of fracture surfaces reveals that fracture occurs at the epoxy‐aggregate interface and within the epoxy itself. Brittle failure specimens show the formation of a powdery residue on the fracture face. The testing and examination suggests that temperature has a significant effect on the ultimate strength and behavior of epoxy mortars.

A general failure criterion for fibrous anisotropic materials is developed in the paper. Since the strength of a lamina should depend on the lamina angle and be symmetric with respect to this angle, the strength of an off‐axis lamina may be expressed as a cosine series. The criterion has the flexibility of any desired degree of accuracy. This capability is needed for complicated materials such as wood and composites. Hankinson's empirical formula for uniaxial loading can be derived by using only the first two terms of the present approach. The accuracy of the criterion is justified through the comparison with experimental data for several material systems subjected to uniaxial and combined loading. The present criterion is also compared with other criteria as well and results are presented in figures. One of the main features of this criterion is that it does not need the shear strength of a material, which is difficult to determine experimentally.

Coal‐burning power plants generate a large amount of fly ash in the United States. A small fraction of the fly ash generated is being utilized in various applications. There is a particular need for further utilization of fly ash. In this paper the results from a recent study on development of a cement composite utilizing relatively large amounts of fly ash are presented. Potential areas of application include waste‐disposal site liners and backfills. The flowable fly ash‐cement sand composite was investigated for strength and permeability characteristics at various stages of maturity. The independent variables considered were: fly‐ash content, sand content, and ratio of water to cementitious materials. Results of this study show that high‐volume fly‐ash composite can be proportioned to obtain compressive strengths as high as 21 MPa (3,000 psi) at 180 days. For applications requiring strengths less than 3 MPa (500 psi), the mixture with fly ash‐cement ratio of 10 and sand‐cement ratio of 20 with relatively high water content may be used. For applications where permeability has to be limited to 10⁻⁷ cm/s, water‐to‐cementitious materials ratio has to be limited to 0.3. The strength of the composite increased significantly with increase in curing time. The splitting tensile strength of the composite was about 7.5% of the compressive strength.

Data collected from tests on 240 nailed joints connecting Douglas‐fir plywood side members to solid‐sawn Douglas‐fir main members were analyzed with the intention of applying the European yield model (EYM) to predict joint behavior under lateral loading. All joints were of approximately similar geometry, with the EYM predicting a failure mode consisting of a single plastic hinge being formed in the nail within the thicker main member. The 5% offset and ultimate loads of the connection were parameters of greatest concern. In addition, a model to predict the embedding strength of solid wood was used to estimate the same parameter for plywood. The results showed that the joint plastic load predicted from the EYM was of a magnitude similar (within 6–28%) to the 5% offset load. The ultimate load was on average approximately 3.3 times the EYM plastic load. However, the high degree of variability found experimentally made deterministic predictions of joint behavior difficult. The study suggested that a model for wood embedding stress used in conjunction with the EYM can be a rational mechanism to estimate the 5% offset load for nailed joints in plywood‐solid‐wood connections.

Recycled poly(ethylene terephthalate), or PET, is mainly recovered from plastic beverage bottles and can be used to produce unsaturated polyester resins. Polymer concrete (PC) made with these resins was investigated for their properties and behaviors at the University of Texas. Thermomechanical properties investigated include strength, Young's modulus, ductility index, Poisson's ratio, coefficient of thermal expansion, shrinkage, and exotherm. Durability properties include chemical resistance, water absorption, and sandblast resistance. Structural behavior of PC reinforced with steel bars and fibers includes load deflection and moment curvature. Overlay behavior includes the effect of thermal cycles on the tensile bond strength of thin PC overlays on portland cement concrete slabs. The properties of PC‐using resins based on recycled PET are comparable to those obtained from PC using virgin resins. Potential applications of such PC materials include precast components; repair of portland‐cement concrete; and bridge, wall, and floor overlays. Resins using recycled PET offer the possibility of a lower source cost of materials for making useful PC‐based products. Also, the recycling of PET in PC would help alleviate an environmental problem and save energy.

Phosphogypsum, a by‐product of fertilizer industry, is the subject of a series of laboratory programs to examine its engineering characteristics “as is” and when combined with Portland cement‐based mixes. Identification tests are aimed at obtaining: physical and geotechnical characteristics; strength as a function of matrix constituents, testing, and curing conditions; relationships between compression and indirect tension; static modulus; fatigue property; sulfate durability; and corrosion protection. It is found that phosphogypsum can be used as a suitable aggregate in concrete for applications such as building products and road construction. Presence of calcium sulfate does not adversely affect the long‐term properties of the cement‐based mixtures containing phosphogypsum.

This paper presents the results obtained from the residual stress relief tests on 21 welded structural steel joints: 17 butt‐welded, two tee, and two corner joint specimens. The A572 grade 50 structural steel plates of two different thicknesses, 15 and 32 mm, were used. All specimens were welded by the submerged arc welding (SAW) process and were designed according to the prequalified welded joints specified by the American Welding Society. In this study, a controlled low‐temperature stress‐relief method was used for residual stress relief. The experimental results show that by using an appropriate combination of the heating temperature, heating distance, and cooling method, the original high‐tensile residual stresses near the weld of the joint can be reduced effectively. The residual stresses before and after the heat treatment were measured by using the blind hole‐drilling method. A reduction of more than 50% of the original tensile residual stresses adjacent to the weld was observed.

Laboratory experiments are performed to study the conditions under which concrete scaling occurs. Induced temperature gradients causes the concrete surface to spall off in sheets, replicating an ubiquitous form of damage to the transportation infrastructure in much of the United States. A mathematical model is developed to simulate temperature gradients in concrete during freeze‐thaw cycles, and the calculated results are in excellent agreement with the laboratory data. By using a finite‐difference model, the rate and depth of temperature changes during surface scaling are predicted.