Journal of Materials in Civil Engineering

Postconsumer plastic chips that cannot be processed for useful applications may end up in a landfill. This constitutes an environmental problem and is considered an additional burden on the already tight landfill space. In this research, plastic chips were used as partial replacement of coarse aggregates in concrete mixtures. The testing program was organized to study the effect of adding plastic aggregates to the concrete in order to reduce the density and gain superior deformation qualities. In this study, plastic aggregates replaced 5, 10, and 15% by mass of coarse aggregates. A total of 198 concrete cubes were made to examine the effect of plastic content and water/cement ratio on the mechanical properties of concrete. The cubes were tested in compression at 1, 7, 14, 21, and 28 days where measurements of deformation were made. The measured load and deformation were used to calculate stress, strain, and modulus of elasticity as related to different plastic content and water/cement ratio. Test results were used to optimize mix design and to establish mathematical relationships between plastic content in the mix and the strength and deformation characteristics of the hardened concrete. Furthermore, digital imaging was employed to scan cross sections of cubes with plastic aggregates to study the orientation of plastic chips in the cube, and to correlate the area of plastics to the increase in durability or the decrease in strength. Test results demonstrated that plastic aggregates are viable in providing the concrete with a high degree of deformability as compared with regular concrete. This characteristic makes the concrete useful in situations where it will be subjected to harsh weather, such as expansion or contraction, or freeze and thaw.

The paper presents a constitutive model developed for high strength concrete with uniform lateral confinement subjected to cyclic axial compression. It is based on the testing program carried out for normal and high strength concrete. Compressive strengths of concrete at the time of testing were 44, 58, 83, and 106 MPa. Uniform confining pressures applied were 4, 8, and 12 MPa. The stress–strain model presented in this paper was developed based on triaxial test results, which were obtained under well-controlled conditions, where direct measurement of axial and lateral strains were possible. Ability to predict the axial as well as lateral strains in confined concrete is a superior attribute of the proposed model. When concrete is analyzed for passive confinement (such as the one provided by reinforcement), estimating the lateral strain is important because the lateral confinement directly depends on it. The proposed model can be used for modeling high strength concrete in seismic analysis of structures, where confining of concrete by reinforcement is essential for ductility.

It is widely known that pavement fatigue life is often greater than that predicted based on laboratory bending beam or indirect tensile fatigue tests. Among many factors contributing to this difference, the effect of sample dimensions on fatigue life can be significant due to the multiphase nature of asphalt concrete. In this research, fatigue tests were conducted on asphalt slabs, which realistically simulate the fatigue cracks in pavements, to investigate crack initiation and propagation. The fatigue crack at the underside of asphalt slabs was identified as a semielliptical surface crack, which is the same type of fatigue crack found in pavements. A three-dimensional finite-element analysis was conducted to evaluate the stress intensity factor. Paris’s law was used to characterize the crack propagation rate. The fatigue crack initiation life and propagation life determined from this research were compared with those calculated using the Strategic Highway Research Program existing parameters and equation. It was found that the two results are significantly different. The factors that may contribute to this difference were discussed.

This paper presents experimental results from a novel study to investigate the feasibility of using a dual sacrificial anode cathodic protection (SACP) system that combined corrosion protection with strengthening. A conductive polymer was used to bond the zinc plates to the concrete surface to form the SACP system, while a single unidirectional carbon fiber-reinforced polymer (CFRP) sheet was bonded to the zinc surface to provide strengthening. However, the aim was not to evaluate strengthening, but to determine if the CFRP interfered with the performance of the SACP system. Four concrete prisms, two of which were strengthened, were tested. The specimens were all placed in a high humidity environment, and their potential and galvanic current measurements were carried out over the entire 295-day exposure period. It was found that the SACP system performed adequately, although there was an apparent decrease in the protective current due to passivation of the zinc plate. Although the potential results from both SACP systems studied (bare Zn plate versus Zn+CFRP ply) were different, the current delivery was similar, indicating little interference between the Zn plate and the carbon fiber ply attached on top of this plate.

Water permeable porosities and thermal conductivity of ceramic construction materials have been experimentally determined in this work. The samples were selected so as to obtain a wide variation in their apparent porosity. To study the influence of porosity on thermal conductivity, thermal conductivities of all the samples were measured in oven dried and water saturated conditions. A model relating porosity with thermal conductivity of these materials is proposed. In the model, two types of pores are hypothesized, namely; enclosed pores and enclosing pores. The three-dimensional steady-state heat transfer through unit cells containing each of the two types of pores, is solved to evaluate their effective thermal conductivity. By using the law of mixture for the random distribution of the type of pores, an equation combining the conductivities of the two cells is framed to get overall effective thermal conductivity of the material, in both dry and saturated states. The experimentally determined values of thermal conductivities reported in literature for some bricks are then compared with those predicted through this model.

The recycling of demolished masonry rubble as coarse aggregate in new concrete represents an interesting possibility at a time when the cost of dumping such material is on the increase. With the number of readily accessible disposal sites around major cities in the world decreasing in recent years and disposal volume and maximum sizes of waste being restricted, the cost of dumping construction and demolition debris has increased substantially over recent years. This cost increase has been further fueled in the United Kingdom and other countries by the introduction of a landfill tax by governments and local authorities for the dumping of such waste. Due to the growing concerns over the environmental impact of aggregate extraction and the continued rise in aggregate demand, it is clear that the building and construction industry is ready to accept recycled and secondary aggregates. This paper provides a review of previous work covering the use of demolished waste, especially crushed brick, as the coarse aggregate in new concrete.

Concentrated load capacities of 18-mm thick one-way simply supported oriented strand board panels together with the mechanical properties of the panels have enabled an assessment of the effect of bending-punching shear interaction on the panel’s concentrated load capacity. Concentrated load capacities of 5.04, 4.44, and 4.29 kN were obtained for 300-, 450-, and 600-mm span panels, respectively. Punching shear capacity of the panels was 6.04 kN. Load capacities based on bending theories of failure were roughly sixty percent of the measured load capacities. An empirical bending-punching shear interaction equation expressed in terms of the bending and planar shear properties and a hypothetical shear perimeter is proposed that enables the load capacities of the panels to be calculated to within roughly 10% of the measured load capacities. Minimal differences between the load capacities of the simply supported and corresponding dowel-fastened panels suggest that the interaction equation is satisfactory for both boundary conditions.

Epoxy-based coatings are used in the rehabilitation and protection against acid attack in industrial and wastewater facilities made of concrete and clay bricks. In this study, the performance of two epoxy-based coatings on sewer grade clay bricks was evaluated using a combination of bonding strength and acid resistant tests over a period of three years. The test results showed that the bonding strength of the epoxy coatings depended on the dry and wet surface conditions of the clay brick at the time of coating. The bonding strength varied from 0.2 MPa to 3 MPa. The coating films effectively reduced the liquid uptake of the coated clay bricks and pinholes influenced the weight gain of the coated clay bricks. There was no direct relationship between bonding strength and acid resistant (weight gain) of the tested coatings. A film model was developed to predict the weight change in coated clay bricks. The mass transfer coefficients of the coatings varied from $0.8\times {10}^{-12}$ to $7.8\times {10}^{-12} m^2/s$ and $1.7\times {10}^{-12}$ to $6.6\times {10}^{-12} m^2/s$ in deionized water and 3% sulfuric acid, respectively.

Many attempts have been focused on the textile reinforced mortar structures. The advantages of textiles are mainly a very good load bearing capacity, excellent ductility, thin size and light weight of components, resistance to corrosion, and no magnetic disturbances. Such structures are expected to have wide application foregrounds. The transfer of forces from reinforcement to mortar is accomplished through a bond. Therefore, understanding and further improving bond properties of textiles in mortar are important. In the paper, bond characteristics of various textiles in mortar obtained from pull-out tests and numerical simulations are shown and compared. The textiles used include carbon, alkali resistant glass and aramid. They were plain and impregnated with epoxy resin. Prestressed and nonprestressed specimens were tested. The experimental results show that epoxy resin impregnating and prestressing can strongly enhance the bond strength. Numerical simulations show good agreement with the experimental results and significantly contribute to a better understanding of the bond characteristics of textiles in mortar.

A comparative analytical study of the average bond strength at failure of reinforcing bars embedded in unconfined normal-strength concrete (NSC) and high-strength concrete (HSC) is undertaken. The analysis makes use of an experimentally derived local bond stress-slip model and considers the progressive bond deterioration along the development/splice length with the increase in bar force. Results of the average bond strength (or development/splice strength) predicted by the analysis showed excellent agreement with experimental data for both NSC and HSC. The analysis predicted a highly nonuniform bond stress distribution at bond failure along the development/splice length, particularly for HSC. Below a certain limit of the development/splice length (about $15-{\mathrm{20d}}_b)\text{,}$ the average bond strength at failure, normalized to $f_c^{\prime 1/2}\text{,}$ is larger for HSC as compared to NSC. However, as the development length increases beyond this limit, the normalized bond strength of HSC becomes progressively smaller than that of NSC. While normalization of the average bond strength to $f_c^{\prime 1/4}$ may underestimate the effect of $f_c^{\prime }$ on the bond strength for short development/splice lengths, it leads to almost identical normalized bond strength results for NSC and HSC within the practical range of development/splice lengths (in excess of $17-{\mathrm{20d}}_b)\text{.}$

The mineralogy of a soil susceptible to sulfate attack was investigated in detail, with particular attention paid to the sulfate and clay minerals. The soil from north Louisiana suffered sulfate attack when stabilized by Type I portland cement. A number of analytical techniques, such as x-ray diffractometry, thermal analysis (thermogravimetry and differential scanning calorimetry), Fourier transform infrared spectroscopy, scanning electron microscopy, and x-ray absorption near edge structure (XANES), were used. Thermogravimetry showed that 7.8% gypsum $({\mathrm{CaSO}}_4\cdot 2H_{2}O)$ was present in the soil from the average of four samples. Quantitative x-ray diffractometry yielded a value of 12.9±1.1% for one soil. XANES indicated that all the sulfur in the soil was present as sulfate phases. Gypsum was found in all size fractions. The clay minerals, kaolinite (highest concentration), illite (intermediate concentration), and smectite (lowest concentration) could be identified with certainty only after the clay fraction was concentrated by removal of gypsum by acid dissolution followed by centrifugation. Kaolinite (5%) could be easily quantified by thermogravimetry but not other clay minerals.

The objective of this work is to develop a user-friendly software, called an “image color intensity analyzer”, and study its application to the relationship between surface color changes and different elevated temperatures of fire-damaged mortar specimens. Images of tested specimens were captured using an ordinary digital camera before being uploaded to a personal computer. Thereafter, the analyzer calculates the intensities of the color components in different color spaces. The relationship between elevated temperatures as well as changes to the color components in different color spaces is studied. This study shows that the intensities calculated from the square root of one-third of the sum of the square of red, green, and blue for sand are useful in determining the highest temperature of the fire-damaged mortar. Results also indicate that the analyzer can quantify color changes of fire-damaged mortar handily and directly.

A method for reusing discarded tires is to process them into crumb-sized particles for use in flexible pavement applications by incorporating crumb rubber (known as crumb rubber modifier) into asphalt mixtures. Understanding of the interaction between rubber and bitumen is an important requirement. The work reported here is the development of a test method suitable for studying the diffusion of bitumen into rubber by determining the rate of bitumen ingression into the rubber (diffusion coefficient) and the solubility of bitumen (concentration at equilibrium or the solubility coefficient). The test method developed is extension of a method employed in adhesion science. The test method has been used to obtain diffusion data of various types of bitumen and two types of rubber from discarded tires to predict the variation of the concentration of bitumen in commercially produced particles of crumb rubber modifier. No such work has been reported in the literature before.