Journal of Materials in Civil Engineering

The absorption characteristics and sorptivity of cover concrete obtained by the initial surface absorption test (ISAT), the covercrete absorption test (CAT), and the sorptivity test have been studied and compared. Two types of concrete, namely ordinary portland cement (OPC) control and low water concrete (LWC) of grade 35 have been tested. The laboratory work has shown close agreement between the ISAT and sorption results but the CAT yields higher results. An analytical model has been developed based on the mechanisms of capillary suction and pressure-driven flow. In this model water entering concrete during the tests is assumed to be concentrated in a well-defined volume. This volume is fully saturated and is separated from the surrounding concrete by a wetting front at which capillary suction occurs. By applying the physical equations for capillary suction pressures and permeability the experimental results are explained in terms of the basic properties of the concrete. The model gives good agreement with the experimental results.

The Dynamic mechanical properties of thermoplastic block copolymer modified asphalt were investigated. A viscosity graded AC-20 asphalt cement and five styrene-butadiene block copolymers with linear and radial structures were mixed at three concentration levels to yield 15 modified blends. The effect of short-term aging on rheological properties was simulated by the rolling thin film oven test (RTFOT) procedure. After establishing the linear viscoelastic range of response through performing stress sweeps, frequency sweeps were carried out at temperatures ranging from 5 to 75°C and frequencies between 0.063 and 188.496 rad/s. Using the time-temperature superposition principle, isothermal response curves were reduced to dynamic master curves of complex modulus and loss tangent. Relaxation spectra were developed by means of an approximate interrelationship between viscoelastic functions. Effects of polymer type and content, and aging condition on viscoelastic response were studied. Addition of polymer was found to substantially broaden the relaxation spectra. With increasing polymer contents, significant changes in the complex modulus and loss tangent at intermediate and low frequencies were observed. At higher frequencies the variations were less apparent and were found to be highly influenced by the aging condition of the modified binders. Evaluation of the measured shift factor data indicated that in all cases a Williams-Landel-Ferry (WLF) equation with universal constants could reasonably represent the temperature dependence of response.

Experimental data for pure bitumens and simplified theoretical models for their deformation behavior are assembled into a single framework that summarizes their steady-state inelastic response to stress. A number of regimes are identified: a low temperature elastic regime, a low temperature plastic regime, a power-law creep regime, and a Newtonian flow regime. Data for a number of pure bitumens are fitted to constitutive equations for each regime. The equations are then used to construct deformation mechanism maps for a particular type of bitumen commonly used in pavement construction in the U.K. These maps relate strength to temperature and strain rate over a wide range of these variables.

The objective of this study was to improve current shear design criteria by establishing a test method for creating a database of beam shear strength of solid-sawn Douglas-fir lumber and correlating it to shear block test results; verifying whether the beam-size equation is a valid correlation between shear strength and beam size for solid-sawn material; and determining whether shear strength is more dependent on shear area, volume, or depth for modeling purposes. Experimental results are presented for 160 shear strength tests on unsplit, green, sawn No. 2 or better Douglas-fir lumber. Five different size specimens, ranging from 38 by 89 mm (2 by 4 in.) to 38 by 337 mm (4 by 14 in.), were tested in five-point beam shear. ASTM D143 shear block minors were cut and tested from each beam. Results adjusted to 12% moisture content were compared with prior research on southern pine and Douglas-fir glued-laminated timber beams. Statistical methods of censored statistics and regression investigated the following possible correlations: shear strength to beam size and beam shear strength to ASTM shear block strength. Results indicate that (1) a five-point test setup can consistently produce beam shear failures over a wide range of beam sizes; (2) shear strength is dependent on beam shear area; and (3) beam shear strength is related to ASTM D143 shear block strength values provided the reentrant corner stress-concentration effects are considered.

Preformed pavement polychloroprene compression seals were analyzed using dynamic shear rheology and numerical analysis to assess the feasibility of using these techniques to develop an improved methodology for designing and characterizing preformed seals, as well as predicting their field performance. The investigation consisted of three phases: (1) dynamic shear rheological analysis of unaged and aged polychloroprene materials to obtain material property input for numerical analysis; (2) numerical analysis of one preformed compression seal web design; and (3) numerical analysis verification through laboratory compression tests of unaged and aged seal materials. The investigational results indicate advanced material modeling capabilities of finite-element analysis coupled with the material properties obtained through dynamic shear rheological analysis provide a significant capability to explore seal performance variations resulting from different joint seal geometries, material compositions, and aging characteristics. The techniques investigated accurately described the deformation of the seal and provided force-displacement relationships, including relaxation with time and stiffening with age. Additional minor refinements in the techniques developed through this investigation would result in a powerful design and field performance predictive model.

Deterioration has been observed in concrete railroad ties, producing a loss of up to 40 mm at the railseat and leaving a rough surface formed mainly by aggregates. This deterioration occurs largely in cold and wet regions of western Canada and northern United States. The purpose of the present investigation was to deduce the processes responsible for this deterioration. Proposed mechanisms included abrasion, erosion, hydraulic pressure, freeze-thaw cycles, and chemical deterioration. Microstructural features associated with each mechanism were explored using laboratory concrete subjected to known deterioration processes or through computer simulations. Microstructural studies utilized scanning electron microscopy and x-ray diffraction. Based on the microstructural evidence, it was concluded that the railseat deterioration is produced by a combination of abrasion and freeze-thaw or hydraulic pressure.

Fiber reinforced plastic (FRP) composites (E-glass, carbon fiber, polyester, and epoxy matrix) were fabricated using “pultrusion,” a cost-effective process for manufacturing fiber/matrix composites. Investigation of the design principles governing civil structures prove that stiffness (elastic modulus)/density rather than strength/density is the most critical property of these materials. Among other variables, large fiber-volume fraction, low void ratio, and fiber straightness are essential for high modulus. The feasibility of rapidly measuring the elastic modulus of pultruded composites during the manufacturing process using acoustic wave velocity was therefore explored. Results were compared with conventional flexure tests and resonant frequency tests. Damping was also comparable to that of steel. Comparison with conventional structural materials reveal that composites currently available in the market are competitive structural materials only if secondary considerations govern the design.

An engineering firm recommended demolition of a multistory brick facade on a building in Charleston, S.C., because the mortar contained chloride in excess of 0.2 by weight of cement. Another engineering firm had a sample of mortar from 10 other buildings tested. Seven of the 10 buildings had mortar chloride content of 0.2 or greater. The level of chloride in mortar in Charleston provides no basis for masonry demolition. A contrary view would require that half the exterior brick masonry in Charleston be demolished.