Journal of Materials in Civil Engineering

Wood is one of the earliest construction materials, and the structural use of wood and wood-based materials continues to steadily increase. In fact, new wood-based materials continue to be developed and successfully introduced into the engineering and construction marketplace. Supporting the increase in use and development of new materials has been an evolution of our understanding of wood as a structural material. The primary aim of this paper is to provide a summary of the status and future of engineered wood and wood-based materials. This paper is not intended to be a comprehensive review of the literature or an all-inclusive state-of-the-art report on all types of wood and wood-based materials. Rather, the focus is on the past, present, and future of engineered wood and wood-based materials for use in civil engineering applications. It also provides a vision for addressing anticipated future research needs. At the conclusion of this paper, the reader may review and consider the recommended actions for advancing the state-of-the-art use and utilization of wood and wood-based materials.

A long-term investigation into the carbonation of concrete exposed to natural weather conditions in Kuwait was undertaken. Forty-four concrete mixes were prepared, and prisms were made and exposed to natural weather after a 28-day period of laboratory air and/or moist curing. Parameters investigated included water/cement ratio, type of cement, type and dosage of admixture, water-curing period, type of curing aid, and special coatings. The admixtures included water-reducers, retarders, and superplasticizers (i.e., high range water-reducers). Carbonation measurements up to a maximum age of 600 days are reported. The results show that the most significant factors influencing concrete carbonation were the use of surface coating, water/cement ratio, water-curing period, and the season when the concrete was initially made and exposed. The use of specialized surface coatings completely prevented carbonation. A decrease in the water/cement ratio and an increase in the water-curing period resulted in a decrease in concrete carbonation. Concrete initially cast and exposed during the winter season exhibited lower carbonation than concrete cast during the summer season. Other parameters, such as the type of cement, admixture, or curing compound used, also influenced the carbonation, although to a lesser extent.

Strain controlled uniaxial tensile and compressive tests of rolled compacted concrete (RCC) are conducted to establish the constitutive relationship of RCC. Complete stress-strain constitutive curves including strain-softening behavior of the material have been obtained. To satisfy the test requirements for obtaining the strain-softening behavior of the material, the stability conditions on specimen parameters and machine rigidity are described based on the concept of strain localization. By using test results of RCC, a 200-m high RCC gravity dam, Longtan Dam, is analyzed for earthquake resistance using the procedure of nonlinear fracture mechanics and the compression-shear failure mechanism for concrete. A safety evaluation of the dam’s ability to resist the design earthquake under different reservoir elevations is performed.

Waste wood sent to landfills represents a potentially valuable resource for construction materials. This paper reports progress in the use of recycled wood aggregate for concrete block. The project goal was to use standard concrete block manufacturing procedures to produce a lightweight block meeting the requirements of ASTM C129 for non-loadbearing concrete masonry. Trial cylinders were made in a laboratory simulation of block plant processes to evaluate admixtures and wood treatments, then promising mixes were used to make several batches of blocks in a commercial plant. Cylinders and blocks were tested for compressive strength, and the blocks were subjected to wet-dry cycling. Results indicate that weight, strength, and durability targets were met. Questions remain regarding the economic performance of the product, and further study is required to evaluate the effect of curing blocks in the uncontrolled exterior conditions typical of the block industry.

This study describes experimental and analytical methods to quantify the structure of air voids in asphalt mixes. An x-ray computed tomography system along with image analysis techniques were used to measure air void sizes at different depths within asphalt mix specimens. The statistical analyses performed validated the applicability of the Weibull model for describing the air void distribution. Consequently, the Weibull model was used to quantify the effect of the compaction effort, method of compaction, and aggregate size distribution on air voids. The air void size distribution in Superpave gyratory compacted specimens was found to exhibit a “bathtub” shape, whereby larger voids were present at the top and bottom parts of a specimen. This shape was more pronounced at higher compaction efforts. The method of compaction was significant in influencing the air void size distribution. Specimens prepared using the Superpave gyratory compactor with different aggregate sizes were found to have noticeably different air void sizes.

This study presents the results of an experimental and analytical comparison of the flexural behavior of a high-strength concrete specimen (no conventional reinforcement) with an average plain concrete cube strength of nearly 65 MPa and containing trough shape steel fibers. Trough shape steel fibers with a volume fraction ranging from 0 to 1.5% and having a constant aspect ratio of 80 have been used in this study. Increased toughness and a more ductile stress-strain response were observed with an increase in fiber content, when the fibers were distributed over the full/partial depth of the beam cross section. Based on the tests, a robust analytical procedure has been proposed to establish the required partial depth to contain fiber-reinforced concrete (FRC) so as to obtain the flexural capacity of a member with FRC over the full depth. It is expected that this procedure will help designers in properly estimating the required partial depth of fibers in composite sections for specific structural applications. Empirical and mechanistic relations have also been proposed in this study to establish the load-deflection behavior of high-strength FRC.

Skilled labor in the concrete industry has been decreasing in recent years, seriously affecting construction procedures and quality. Therefore, it is necessary to set up a rational mix design and construction procedure. The writers have done extensive modeling of fresh concrete by distinct element modeling (DEM), assuming it to be a two-phase material. So far, research has been limited to qualitative simulation because of the difficulty of defining mortar DEM parameters. In this research, the mortar parameters are defined from rheology. Then, a quantitative simulation is proposed. Slumping behaviors of fresh concrete are simulated. All the processes involved in a shotcrete are numerically modeled, and shotcrete simulation is carried out. The simulated fresh concrete and shotcrete result are of the same order as the experimental ones. A very few comparisons between experimental and simulated results are shown due to the unavailability of experimental data.

Wind, earth pressure, and earthquakes acting on a building generate bending effects and produce shear stresses in load bearing masonry walls. Stress and strain responses during shearing of masonry joints indicate unrecoverable shear and normal deformation that demand use of a constitutive model specifically developed for joints. In this study, an elasto-plastic joint constitutive law is proposed to model the shearing behavior of joints in load-bearing masonry walls. The brick-mortar bed joints were sheared using a shear box test. The physical parameters of the model were obtained from the experimental data. The load-displacement response observed experimentally was analyzed using the proposed constitutive law. The model appears to predict the shearing behavior of brick-mortar bed joints reasonably well. The study presented herein provides a basis for using an analytical method for determining shearing displacement response of brick-mortar bed joints by applying an elasto-plastic constitutive law for joints and determining its parameters from the shear testing of brick-mortar bed joints.

A total of about 210 cylinders and cubes of five different sizes and aspect ratios made from eleven batches of concrete were tested in direct compression to establish the interrelationships between their strengths. The range of concrete strengths considered was between 20 and 100 MPa. All specimens prepared from each batch of concrete were cured under identical conditions before testing at the same age. An analysis of these data together with those generated earlier at the National University of Singapore has revealed that the ratio of standard cube strength to that of other specimens decreases with an increase in the level of concrete strength. Also, a decrease in either the size or the aspect ratio of specimens leads to a decrease in this ratio. Expressions relating the compressive strengths of cylinders of two different sizes and two different aspect ratios, and of smaller size cubes with standard cube strength, are presented. These expressions may be combined to obtain useful interrelationships between the strengths of any two types of specimens.

Anisotropic elastoplastic models to simulate the mechanical behavior of ferrocement plates are proposed. These models use elastic and inelastic properties derived from simple in-plane tension and compression experiments. Mindlin plate theory in conjunction with a layered approach is employed for analysis. Two different mathematical models, the homogeneous layered model and the mortar-ferrocement layered model, are considered. The former assumes all the layers to possess identical anisotropic material properties. The postelastic behavior is modeled using the anisotropic Hoffman criterion. In the mortar-ferrocement layered model, the plate is divided into “mortar” and “ferrocement” layers. The mortar layers are assumed to be isotropic and their postelastic behavior is simulated using isotropic Hoffman criterion. The ferrocement layers are modeled using two approaches: in the first, they are assumed to be transversely isotropic (transtropic) and in the second an orthotropic material idealization is employed. The analytical predictions are found to compare well with the experimental results. The mortar-ferrocement layered model with orthotropic ferrocement layers performs the best. It is concluded that a single set of material properties can be used to simulate the behavior of ferrocement plates under in-plane as well as out-of-plane loading.

Two methods, a three-parameter (work-hardening) model and a pseudostrain energy model, were used to characterize permanent deformation-related damage potential of asphalt mixtures. The three parameters were calculated by fitting a curve that describes permanent strain accumulation during repeated load compressive testing. The pseudostrain energy was calculated using the linear viscoelastic constitutive equation. Both methods are appropriate and predict permanent deformation and tertiary damage in asphalt mixtures due to plastic deformation and microcrack development. The effects of a waste carpet coproduct and hydrated lime on permanent deformation were evaluated using the two techniques. The coproduct reduced damage potential in both a dense-graded mix and in a mix designed to exhibit early tertiary damage (tender mix). The coproduct was effective with two compositionally different bitumen within each mixture. Hydrated lime was effective in reducing tertiary damage potential in the dense-graded mixture, but its effectiveness was mixture and bitumen dependent.

Some properties of concrete with sawdust ash (SDA) as a replacement for ordinary portland cement (OPC) are investigated. The compressive strength of specimens with replacement levels ranging from 10 to 30% cured for periods of 3–90 days showed a decreasing strength with higher ash content. The 28-day split tensile strength of SDA concrete specimens showed a similar trend. The SDA concrete was observed to gain rapid strength at later ages, indicating a pozzolanic activity of the ash. Although only concrete with a 10% replacement level attained the 20 N/mm² designed strength at 28 days, test results indicate that SDA concrete can attain the same order of strength as conventional concrete at longer curing periods.

An experimental investigation was conducted to evaluate the split tensile load-deformation strength and toughness properties of a granular soil chemically stabilized with cement and fly ash, and mechanically reinforced with recycled plastic strips [high-density polyethylene (HDPE)] obtained from postconsumer milk or water containers. The primary objective of this research was to evaluate if a modest amount of reinforcing fibers derived from recycled plastics can enhance the mechanical performance of a lean cementitious composite by improving the split tensile strength and the postpeak load carrying capacity. As an extension to the ASTM C 496 procedures for split tensile tests, two lateral linear variable differential transformers were attached to measure the tensile deformation of the horizontal diameter due to loading in the orthogonal direction; this method permitted an evaluation of the fiber toughening action under split tension. Two major groups of mixes were used for the study. The first group was stabilized with only 2–5% cement, while the second group contained 10% cement (by weight); several specimens also contained an additional 2–10% ASTM class C fly ash. Fiber-reinforced specimens contained 0.25% (by weight) to 0.80% (by weight) of recycled HDPE. A dimensionless toughness index and a fiber factor were defined in order to quantify the improvement in strength and toughness characteristics. It was found that the inclusion of HDPE fibers does not meaningfully improve the tensile strength, but significantly enhances the overall toughness of the composite. Results indicate that the test procedure, and the toughness index and fiber factor proposed in this study can be utilized to evaluate the performance of a fiber-reinforced stabilized soil for geotechnical and pavement applications.

The effects of exposure to different environmental conditions on the bond strength between a thermosetting adhesive and concrete were investigated. In particular, the influence of temperatures higher than room temperature and the presence of water on adhesion properties were studied. The results were compared with those relative to specimens tested in ordinary conditions. The increase of test temperature caused a reduction of the bond strength irrespective of the concrete used. The effect of temperature was almost completely reversible because the bond properties were recovered when the temperature was lowered. The presence of water also caused a decrease in adhesion properties, at least to a minor extent. These conditions also affected the mechanism of failure occurring in the samples. On the basis of the obtained results, it is suggested that the environmental conditions in which the adhesive is employed be carefully examined to avoid the occurrence of unexpected failure of the bond and compromising the effectiveness of the repairing technique.