Journal of Materials in Civil Engineering

Concrete cover, concrete quality, and bar size have a significant effect on corrosion initiation and corrosion cracking. This paper attempts to quantify the effect of these three parameters in providing corrosion protection to reinforcing steel. It is found that the cover‐to‐bar‐diameter (c/d) ratio is a more definitive protection parameter against corrosion cracking than either cover or bar diameter separately. In view of the importance of c/d ratio, clear cover specifications without consideration of the bar size leads to inadequate and misleading design for corrosion protection, especially in concrete where internal chlorides are present in concrete from the time of manufacturing, making the corrosion propagation time prior to cracking an important phase in the service life of structures. A concept of corrosion cracking resistance factor, ${\mathrm{cf}}_c^{\prime }/d$ or c/dw incorporating cover, bar diameter, and concrete quality either in terms of strength $\left(f_c^{\prime }\right)$ or water‐cement ratio (w) has been developed to quantify the relative corrosion protection provided by a particular set of detailing and strength parameters.

The resilient modulus is used as a fundamental input parameter in the application of layer theory in flexible‐pavements design. The test for determining the resilient modulus is a repeated‐load indirect tension test in which specimens are loaded then unloaded diametrally and the recoverable strain is measured. The test procedure is standardized and documented by the American Society for Testing and Materials (ASTM) in ASTM D4123. The statistical variability in the test for determining the resilient modulus is important for design purposes. There exist two sources of variability in the standard test procedure set by ASTM. The first source is observed where different specimens from the same mix have a different value of the modulus. The second source is due to the testing method where the cylinders are tested diametrally, and the random choice of axis can be another source of variability within the same specimen. Also, since ASTM D4123‐90 recommends an acceptable range for the load amplitude, the choice of the load amplitude may introduce some variability. In this paper, several specimens of asphaltic concrete were cast from the same mix. Each specimen was tested on three different axes, under four different loads, and the resilient modulus was measured, thus reflecting both the specimen‐to‐specimen and the axis variability. The two sources of variability were combined statistically to obtain an estivate of the coefficient of variation (COV) in measuring the resilient modulus. The resulting estimate of the variability can be combined with other variabilities that arise in practice, to obtain an estimate of the total variability that should be considered in designs based on the measured resilient modulus.

The properties of concrete and concrete masonry using municipal solid waste (MSW) ash as fine aggregate were studied. Mass‐burn combined ash and refuse‐derived‐fuel (RDF) bottom ash were studied. The properties included com‐pressive strength, expansion, time of set, unit weight, leaching characteristics, and gas generation by the mixtures. These ashes were not suitable for use in concrete because of low strength and cracking caused by gas generation. Some concrete‐masonry specimens containing ash had adequate strength but had bad smell and cracking and spalling problems. Mass‐burn ash produced higher concrete and concrete‐masonry strengths than RDF ash. EPTOX tests showed that leachate from the MSW concrete or concrete masonry did not exceed toxicity limits.

Durability and leachate characteristics of concrete containing municipal solid waste (MSW) fly ashes from both refuse‐derived‐fuel (RDF) and mass‐burn plants are studied. Performance of the concrete varies significantly depending on the type of MSW fly ash it contained. Concrete containing MSW fly ashes with high loss on ignition values can be entrained with 6–7% air, but high dosages of air‐entraining admixture are needed. Some of the RDF fly‐ash concretes show good freeze‐thaw durability. Freeze‐thaw durability decrease as the amount of MSW fly ash increased. Mass‐burn fly‐ash concrete show superior resistance to surface scaling from deicing salts while RDF fly‐ash concrete exhibits poor scaling resistance. MSW fly ashes and concrete containing them have high levels of chloride ion. EPTOX tests show that none of the leachates from the fly‐ash concretes exceed toxicity limits.

A commonly used mathematical model to predict the lateral load‐slip $(P‐\Delta )$ behavior of nailed joints in wood is expanded in this study to account for several important characteristics of the connection. Nonlinear curve‐fitting procedures are used to develop prediction relationships for parameters A and B in equation $(P=A{\log }_{10}[1+B\Delta \left]\right)$ for a variety of joint material and geometric characteristics. $P‐\Delta$ curves are experimentally obtained for 292 single‐shear nailed joints made with main and side members consisting of seven hardwoods indigenous to the Amazonian region of Brazil, four diameters of common wire nails (2.87, 3.33, 3.76, and 4.07 mm), three nominal moisture contents (6, 12, and 18%), and six nominal side‐member thicknesses (12, 19, 25, 31, 38, and 50 mm). The specific gravity (oven‐dry volume basis) of individual specimens ranges from 0.36 to 0.85. This range is larger than would be found among temperate zone species customarily used in construction. A contemporary statistical software package is used to perform regression analyses to predict A and B from 33 functions of various combinations of the nail diameter, side‐member thickness, and main‐ and side‐member specific gravity. Results indicate that the best prediction equation models the shape of the experimental curves with reasonable accuracy. When the estimated parameters are used to predict the $P‐\Delta$ curves for the 292 test joints, an average mean deviation of about $-11\%$ was found. The negative value suggests that the model tended to overpredict joint stiffness.

Design methods for tapered members of multiple materials with nonrectangular cross sections are not available. This finite‐element study of straight, single‐tapered I‐beams was conducted to aid in developing a rational design method for nonprismatic, I‐shaped structural members of layered orthotropic materials. Particular emphasis is placed on wood composites. Taper geometry $(0\le \theta \le 6.3°)$ is considered in concert with the elastic constants of the web substrate. Comparisons of the stresses and deflections in a prismatic beam and a tapered beam of the same average depth and having the same elastic properties for the web are used to identify potential design considerations. The bending, vertical, and shear stress maximums are greater in the tapered beam than in the prismatic beam. In addition, the stresses are distributed differently if the beam is tapered rather than prismatic. For example, the maximum shear stress is not necessarily in the web. Deflection of the tapered member is 19% greater and occurs at 0.43L rather than at midspan.

TO use steel fiber‐reinforced concrete in structural applications, the complete stress‐strain behavior of the material in compression is needed. This paper presents the experimental stress‐strain behavior of fiber‐reinforced concrete with compressive strength ranging from 5 ksi to 12 ksi (35 MPa to 85 MPa). Three fiber volume fractions of 50 lb/cu yd, 75 lb/cu yd, and 100 lb/cu yd ($30\mathrm{kg}/m^3\text{,}$ $45\mathrm{kg}/m^3\text{,}$ and $60\mathrm{kg}/m^3$) and three aspect ratios of 60, 75, and 100 are investigated. The influence of the fiber‐reinforcing parameters on the peak stress, corresponding strain, the secant modulus of elasticity, the toughness of concrete, and the curve shape are reported. A simple equation is proposed to predict the complete stress‐strain curve. Addition of steel fibers to concrete with or without silica fume effectively increases the toughness of such concrete. A marginal increase in the compressive strength, the strain corresponding to peak stress, and the secant modulus of elasticity is also obtained. The increase of silica‐fume content renders the fiber‐reinforced concrete more brittle then non‐silica‐fume concrete. The equation proposed to generate the complete stress‐strain curve for non‐silica‐fume fiber‐reinforced concrete provides a good correlation between predicted and experimental results.

The results of water-permeance tests complying with ASTM E514 on brick veneer walls with metal stud backups are reported. The water permeance tests were a part of an experimental program designed to evaluate the performance characteristics of the wall system. The project included flexural testing of full-scale wall panels. Six full-scale walls were tested, three with positive pressure and three with negative pressure. The water-permeance tests did not show any close correlation between water penetration and the level of load to which the walls were previously subjected.