Journal of Materials in Civil Engineering

In steel fiber-reinforced composites materials, fiber and matrix are bonded together through a weak interface. The study of this interfacial behavior is important for understanding the mechanical behavior of such composites. Moreover, with the outcome of new composites materials with improved mechanical properties and advanced cement matrices, such in the case of steel fiber reinforced self-compacting concrete, the study of the fiber/matrix interface assumes a new interest. In the present work, experimental results of both straight and hooked-end steel fibers pullout tests on a self-compacting concrete medium are presented and discussed. Emphasis is given to the accurate acquirement of the pullout load versus end-slip relationship. The influence of fiber embedded length and orientation on the fiber pullout behavior is studied. Additionally, the separate assessment of the distinct bond mechanisms is performed, by isolating the adherence bond from the mechanical bond provided by the hook. Finally, analytical bond-slip relationships are obtained by back-analysis procedure with an interfacial cohesive model.

Increased loads on hot-mix asphalt (HMA) pavements have necessitated the development of new-generation asphalt mixture designs that rely on stone-on-stone contact among coarse aggregates in resisting and distributing applied loads. These stone-on-stone contacts, however, promote localized internal stresses that could cause aggregate fracture. Therefore, it is imperative that methods are developed to analyze the contribution of the coarse aggregate structure and properties to HMA performance during mixture design. This paper introduces an approach that combines the discrete element method (DEM) and image processing techniques to analyze the combined effects of aggregate gradation, shape, stiffness, and strength on HMA resistance to fracture. The DEM input parameters were determined based on measuring aggregate and HMA properties. Consequently, the model was used to quantify the internal forces in asphalt mixtures and determine their relationship to aggregate fracture which cannot be accomplished by conventional experimental methods. The model was successful to large extent in representing the influence of variability in aggregate properties and blending two sources of aggregates on mixture strength. The results showed that the required aggregate strength and optimum blending limits to achieve certain mixture strength are dependent on mixture design.

This study investigates the effect of thermal cycling on the performance of concrete beams retrofitted with CARDIFRC, a new class of high performance fiber-reinforced cement-based material that is compatible with concrete. Twenty four beams were subjected to 24 h thermal cycles between $25$ and $90°\text{C}$ . One third of the beams were reinforced either in flexure only or in flexure and shear with conventional steel reinforcement and used as control specimens. The remaining sixteen beams were retrofitted with CARDIFRC strips to provide external flexural and/or shear strengthening. All beams were exposed to a varied number of 24 h thermal cycles ranging from 0 to 90 and were tested in four-point bending at room temperature. The tests indicated that the retrofitted members were stronger and stiffer than control beams, and more importantly, that their failure initiated in flexure without any signs of interfacial delamination cracking. The results of these tests are presented and compared to analytical predictions. The predictions show good correlation with the experimental results.

This study investigated the curing mechanism of foamed asphalt mixes. Various laboratory strength and stiffness tests were performed on mixes with various asphalt and portland cement contents, and the specimens were subjected to two relatively extreme curing conditions. It was found that portland cement enhances certain properties of foamed asphalt mixes by strengthening the mineral filler phase, with the curing mechanism similar to that of typical cement treated materials. The curing mechanism of foamed asphalt mastic is primarily related to water evaporation. The bonding between asphalt mastic and aggregate particles cannot fully develop until most of the water retained at the interface evaporates. This bonding, once formed, is only partially damaged by reintroduced water. This proposed mechanism was supported by observations of fracture faces on tested specimens. A long-term curing study confirmed the validity of this mechanism regardless of the curing duration. Standard curing procedures are proposed for use in project level mix design and evaluation based on the findings.

This paper is based on an expert system for inspecting adhesive ceramic wall or floor tiling (ACT), which includes all the anomalies that may occur in ACT as well as their most probable causes. To support diagnosis, a classification of in situ inspection and testing methods is presented as well as the files that characterize them. Diagnosis tools are complemented with a correlation matrix anomaly/test method. The repair of anomalies and the elimination of their causes are supported by a classification of the repair techniques, for each one of which a characterization file is presented and by a correlation matrix anomaly/repair technique. The ACT inspection system was validated through a series of standard inspections of 155 ACT cases, also described here. Data concerning inspection, diagnosis, and repair of each anomaly type were condensed into individual anomaly files. The expert system proposed is an essential tool for the implementation of management systems for buildings, paving the way for more objective periodical inspections and for a standardization of their procedures.

This research studies the potential of using disposed fly ash to add up or partially replace Portland cement Type I in ground improvement by cement column technique. The strength characteristic of cement-fly ash admixed Bangkok clay was investigated by means of a series of unconfined compression tests, paying special attention to the influence of ground fly ash in this mixture. From testing results, the unconfined compressive strength and elastic modulus improved with an increasing of fly ash content. With the cement portions of greater than or equal to 10%, ground disposed fly ash could be employed as a pozzolanic material for partial replacement of cement in cement column construction. Based on the equivalent cementitious material content concept, an empirical equation relating the efficiency factor, $\alpha$ with mixing proportions was proposed. Then, together with this proposed efficiency factor, strength prediction of cement-fly ash admixed clay by Feret’s equation and Abram’s law were carried out and discussed.

This paper presents the results of a study on the effect of high temperatures on the mechanical properties of high-strength concretes. Mixtures were prepared with water to cementitious material ratios of 0.40, 0.35, and 0.30 containing silica fume at 0, 6, and 10% cement replacement. After heating to 100, 200, 300, and $600°\text{C}$ , the compressive strength, the splitting tensile strength, and the corresponding ultrasonic pulse velocity were measured. A substantial loss of strength was observed for all compositions at $600°\text{C}$ , particularly the silica fume concretes in spite of the superior mechanical properties provided by silica fume at room temperature. The average residual compressive and splitting tensile strengths of the concretes at $600°\text{C}$ were 30 and 25% of the room-temperature strengths, respectively. It was found that the rate of the splitting tensile strength loss is higher than the rate of the compressive strength loss at elevated temperatures and that the ultrasonic pulse velocity measurements slightly underestimates the residual strength of the high-strength concretes after exposure to temperature over $200°\text{C}$ .

The low-cycle fatigue behavior of ASTM A706 and A615 Grade 60 (420 MPa) deformed reinforcing steel bars were evaluated experimentally. Although this study was initiated to evaluate the low-cycle fatigue of reinforcing bars in precast hybrid frame connections, the conclusions presented here may also apply to other relevant applications. Laboratory tests were performed under strain-controlled cyclic axial loading with nonzero mean strains. The deformed bars were subjected to constant-amplitude sinusoidal strains ranging from zero to peak strains that varied between 2 and 8% in different tests. All tests were performed on unmachined bar specimens. The experimental data were analyzed and compared with existing low-cycle fatigue models. Such models relate the total and plastic strain ranges to the number of cycles to failure. Relationships for calculating the tensile and compressive stresses corresponding to maximum strains are proposed based on the experimental results. Equations that relate dissipated energy to strain amplitudes and the number of cycles to failure are developed. This study demonstrates that the low-cycle fatigue responses of ASTM A706 and A615 mild steel bars are similar even though their monotonic ductility ratios are very different. The proposed low-cycle fatigue relationships for both ASTM A706 and A615 mild steel bars can be used to calculate maximum permissible strains in applications such as the precast/prestressed hybrid frames. The prediction of bar fracture due to low-cycle fatigue is an important consideration in the seismic design of reinforced and precast/prestressed concrete structures.

Concrete is the most widely used material in construction industries. Therefore, it is necessary to understand and when possible, improve the efficiency of a concrete production process. Statistical process control is generally applied to gain information about variation in the manufacturing process. Control charts can be implemented to monitor the various processes involved in the production, the delivery and construction of concrete. When historical data are available on various projects, better insight into operational procedures can be obtained through the use of control charts. This paper studies a series of statistical analysis procedures to analyze the compressive strength of concrete. The proposed method is based on combining the cumulative sum (CUSUM) control chart and a run chart (CUSUM-run chart) for early detection of shifts in the process mean. The combined charts address both the consumers’ and the producers’ perspectives. The CUSUM-run chart can aid the consumer in making decisions about accepting or rejecting a strength test. In addition, the producers (concrete manufacturers) can use the chart to determine if the monitored process is out-of-control and subsequently attempt to identify the possible causes for the out-of-control situation. By identifying assignable causes of the out-of-control process, the producer can then improve the manufacturing process by reducing product variation, unnecessary waste, or over-designed concrete mixtures. The CUSUM-run chart is also beneficial in that it can often indicate when the strength of mixture is less than the minimum acceptable level very quickly. The delay in detecting an unacceptable strength can result in more penalties, project delays and increased associated costs.

The log building industry favors simple to install mechanical connections between log layers, also referred to as log courses, to facilitate fast and efficient construction. In active seismic regions, lag screws are commonly used: however, research is lacking on how these connections between log courses perform in monotonic and reverse-cyclic loading scenarios. For the current study, 406-mm-long logs were used to fabricate connection test specimens in a single-shear configuration to mimic a typical lag screw layout used in log shear wall construction. The intent of this study was to develop baseline data on these connections to relate log connection performance to full-scale log shear wall performance. A preliminary study of four commonly used lag screws of different sizes was conducted to assess the monotonic performance within log connections. Predictions of design capacities were calculated using the National Design Specification for Wood Construction which is based on derived equations from the European yield model. Predicted NDS design capacities were compared to experimental data. Design recommendations for deriving appropriate fastener spacing were provided along with fabrication parameters that were based on observed failure mechanisms. Tested connections exhibited high ductility, which is considered a positive attribute for seismic resistance, although reverse-cyclic tests revealed failures due to low-cycle fatigue of the lag screws, leading to prevalent cyclic stiffness degradation as displacements were increased.

There is evidence that the presence of certain microfine coatings $\left(⩽75\mu \text{m}\right)$ on coarse aggregates encountered in actual field conditions and accepted for state projects has adverse consequences for the properties of hardened concrete. The purpose of this research was to investigate the influence of natural coarse aggregate coatings on physical properties of concrete and to establish how each of the three common monitoring tests (ASTM C117, Caltrans Test No. 227, and AASHTO TP57) predict the influence of these coatings on the quality of the resulting concrete. Seven mixtures of concrete were prepared with coarse aggregate containing two types of coatings: natural field-coated aggregates, and manufactured coated samples of dust and clay fines. The effects of these coatings on concrete performance were assessed by comparing the relative changes in the physical and mechanical properties of the concrete against concrete made with washed aggregate. The study confirmed that the extent and nature of the impact depend on the quantity and nature of the microfine, and therefore the current ASTM C117 is not an adequate monitoring tool.

The previous work of another group of researchers found that the modulus of tension, flexural, and compression increased with increasing percentage by volume of fly ash. They also documented that the viscosity of the composite increased exponentially with increasing percentage by volume of the filler. The viscosity increased sharply when the percentage by volume of reinforcer is between 35 and 50%. They failed to mention the highest percentage by weight of fly ash that could be added to the resin to get the highest mechanical properties while still ensuring that the composite could be cast into molds with ease. This project attempts to find out the optimum percentage by weight of cement hollow spheres (SLG) in vinyl ester resin as far as yield strength, tensile strength, Young’s modulus, and Poisson’s ratio of the composite are taken into account. The research found that 33% by weight of filler is a favorable and convenient percentage by weight of SLG to use because up to this percentage by weight of reinforcement, the mechanical properties like modulus of tension are increasing with the increase in percentage by weight of filler while at the same time the viscosity is not high enough to prevent ease of casting the composite into molds.