Journal of Materials in Civil Engineering

The purpose of this paper is to evaluate the effect of aggregate shape on the chloride diffusivity of concrete through laboratory experiments and theoretical analysis. In the experiment, three types of crystal glass spheroids with aspect ratios of 1, 2, and 3 are used as coarse aggregate. The experimental results show that the chloride diffusivity of concrete decreases with an increase in aggregate aspect ratio. When the coarse aggregate volume fraction is equal to 0.1, 0.2, and 0.3, the chloride diffusivity of concrete at an aggregate aspect ratio of 3 is, on average, smaller than that at an aggregate aspect ratio of 1 by 5.29%, 11.4%, and 19.6%, respectively. An analytical approximate is derived for the chloride diffusivity of concrete with spheroidal aggregates and verified with the experimental results. The analytical approximate can predict the chloride diffusivity with an average relative error of less than 8%.

Sand mix interlayers are one of the most widely used stress-absorbing types of interlayers employed for concrete overlays and concrete bridge decks. Most of the available research focuses on the function of sand mix interlayers in terms of mechanics and ignores their ability to mitigate thermal cracking, which is one of the main distresses in pavements. To address this deficiency in the current body of literature, this study analyzes the effect of a sand mix interlayer on thermal cracking in overlays. This research examines the asphalt mixture, sand mix and concrete materials in terms of their contraction performance. The stress and strain states of the structures with and without a sand mix interlayer are determined using a strain gauge and are simulated using ABAQUS. The results show that after adding a sand mix layer, the stress state of the asphalt mixture is much closer to its stress state without any constraint. The inclusion of the sand mix layer decreases the tension stress at the bottom of the asphalt layer, so that the distance between thermal cracks is allowed to increase and the number of thermal cracks decreases, which is good for the layered structure.

Controlled low strength material (CLSM), as defined by the American Concrete Institute (ACI) Committee, is a self-flowing cementitious material consisting typically of portland cement, fine aggregates, supplementary cementing materials, and water. In this present experimental study, industrial by-product, namely, ground-granulated blast-furnace slag, is used as a constituent material in CLSM. Mixture proportions were developed for CLSM containing the industrial by-product (GGBS) and were tested in the laboratory for flow and unconfined compressive strength properties. The cardinal aim is to analyze the experimental data generated to formulate a phenomenological model to arrive at the combinations of the ingredients to produce CLSM to meet the desired flow and strength. An independent set of data is generated to examine the validity of the phenomenological approach.

The sewage treatment plants generate, as by-products, large amounts of sludge containing harmful elements to the environment. This paper investigates the possibility of using 10% of sewage sludge by weight in pavement base layers. The soil stabilization technique was used to improve the residue properties to satisfy the minimum requirements for road bases. The intent of this stabilization technique was to use conventional additives as cement, lime, and emulsion. The main objective was to evaluate the strength behavior of the modified soil. Sludge-soil mixtures with different additive contents (2, 4, 6, and 8%) were prepared for testing. The modified soil samples were subjected to compaction, and then tested for the following parameters: California bearing ratio, unconfined compressive strength, indirect-tensile strength, resilient moduluså, and deterioration tests. Mechanical tests were used to estimate the optimum mix design. Test results indicated that the stabilization of mixtures of soil with sewage sludge has the potential to be used in the pavement industry.

Asphalt mixture is a heterogeneous, composite material consisting of aggregate, mastic, and air voids. Analysis of laboratory tests such as the dynamic complex modulus assumes that this material can be dealt with as a homogeneous material while overlooking the particulate nature of this composite. Because of the limitations of the elastic continuum theory, pavement engineers have recently paid considerable attention to the use of advanced modeling techniques for simulating the realistic behavior of asphalt mixtures. The objective of this study is to develop a three-dimensional (3D), heterogeneous model to describe the response of asphalt mixtures in the dynamic complex modulus test using an X-ray computed tomography image–based finite-element (FE)-modeling approach. Experimental testing results for two superpave mixtures, including one conventional hot-mix asphalt and one warm-mix asphalt, were used to validate and calibrate the developed FE models. Acceptable agreement between laboratory-measured and model-predicted dynamic modulus test results was achieved. Results of the developed FE models at different temperatures indicated that most of the deformations during the dynamic modulus test are derived from the mastic. In addition, the asphalt mastic had more influence than the aggregates on the results of the dynamic complex modulus test.

The effect of sustained compressive and tensile loads applied to concrete with fly ash and blast furnace slag on chloride diffusion coefficient was evaluated in this study. The experimental results indicated that with the increase of compressive stress, the chloride diffusivity coefficient initially decreases, and with a further increase in stress level, the chloride diffusivity coefficient of concrete increases. The chloride diffusivity coefficient increases with the increase of tensile stress applied to the concrete. In this paper, the maximum increase in chloride diffusivity coefficient is 70% when tensile stress level is 66.1%. The relationship between chloride diffusivity coefficient and stress is proposed for predicting the chloride diffusion coefficient under different loading states.

This paper summarizes the environmentally assisted degradation of the bond between steel and carbon fiber–reinforced polymer (CFRP) composites through analysis of the mechanical performance of loaded and unloaded steel/CFRP double strap joints exposed to various harsh environments such as elevated temperatures, seawater, cyclic temperature and humidity, and ultraviolet (UV) radiation. It was found that both joint stiffness and strength significantly decreased by up to 80% when tested at elevated temperatures near to or greater than $T_g$ of the adhesive used. The mechanical properties reduced by about 20% when exposed to seawater for up to 1 year. Although no significant reduction in stiffness and strength were found when the unloaded joints were exposed to cyclic temperature between 20 and 50°C with the added presence of humidity, the loaded joints catastrophically failed during the exposure, showing that the combination of load, temperature, and moisture was the most critical scenario. In addition, UV exposure also led to a decrease in strength but an increase in stiffness for the unloaded joints, caused by the postcuring with the heat supplied by the UV rays.

A performance test, rather than an empirical test, to evaluate rutting susceptibility is needed to accompany current volumetric property requirements of airport hot mix asphalt (HMA) designed using a superpave gyratory compactor. The new performance test will provide a level of confidence that pavement constructed using a selected HMA mixture will function according to its design. This paper presents results from a laboratory study to identify a performance test for accepting hot asphalt mixtures for constructing airport pavements designed for high tire pressure traffic. Performance tests intended to indicate rutting susceptibility were performed on 34 HMA mixtures. Twenty-nine of these mixtures met all aggregate and volumetric property requirements for airport pavement construction; the remaining five mixtures were designed with excessive percentage of natural sand (30%) as rut-susceptible mixtures. Results from asphalt pavement analyzer (APA), triaxial static creep, and triaxial repeated load tests are presented. Statistical analyses performed on the results indicate that the rate of increase in permanent strain and the flow time value determined from triaxial static creep testing provide the strongest correlation to APA simulated traffic rutting.

Hydrated cement–treated crushed rock base (HCTCRB) is produced by adding 2% Portland cement (by mass) to a standard crushed rock base (CRB) at an optimum moisture condition. The unique production process for HCTCRB is different from that of a common cement-treated base in that a remixing process is performed after the hydration of cement, preventing cementitious bonding to maintain the unbound material characteristics with an improvement in material engineering properties. This paper presents the resilient modulus ($M_R$) and permanent deformation (PD) characteristics of HCTCRB after variable hydration periods, water addition during compaction, and dryback. The difference in material hydration periods affected the performance of HCTCRB. However, in this study, a consistent performance trend with various hydration periods could not be found. Moisture contents have a major influence on the properties of HCTCRB. The results indicate that a higher moisture content increases the PD and decreases the $M_R$ of this material. The addition of more water during compaction caused inferior PD and $M_R$ performance even though the samples achieved a higher dry density. A dryback process to achieve a dryer condition can improve material performance. After samples were subjected to a dryback process, it was found that samples prepared by adding water during compaction showed a decrease in material performance compared with samples that were compacted without additional water. Thus, the amount of water added to mixes during compaction must be controlled.

The role of filler effect and pozzolanic reaction of biomass ash on hydrated phase and pore size distribution of blended cement paste was studied. Rice husk ash (RHA), palm oil fuel ash (POFA), and river sand (RS) were ground to two fineness values, and used to replace Type I portland cement (OPC) at 0, 20, and 40% by weight of binder. A water to binder ratio of 0.35 was used. The compressive strength, pore size distribution, and thermogravimetric analyses of the blended cement pastes were investigated. Partial replacement of OPC with fine RHA and POFA at a dosage of 20% by weight of binder resulted in pastes with higher compressive strengths than that of OPC paste. The compressive strengths of RHA paste were slightly higher than those of POFA pastes at the same age. The differences between mass losses (at 30–450°C) of RS and RHA (or POFA) blended pastes at the same fineness, curing time, and replacement rate were due to the pozzolanic reaction, which increased in accordance with particle fineness and cement replacement rate. In addition, the weight losses (at 30–450°C) due to the pozzolanic reaction were higher than those due to the filler effect. The use of fine RHA and POFA enhanced the pozzolanic reaction, and reduced the average pore diameters of pastes.

This study addresses the use of a stress-to-strength ratio as a failure criterion for thermal cracking. Restrained cracking frame specimens and accompanying match-cured concrete cylinders were tested to determine the ratio of stress-to-splitting tensile strength at cracking. A stress-to-splitting tensile strength ratio of 0.57 was found to give a 50% probability of cracking and lognormal standard deviation of 0.16 when splitting tensile cylinders sized $100\times 200\mathrm{mm}$ ($4\times 8\mathrm{in.}$) and $150\times 150\mathrm{mm}$ ($6\times 6\mathrm{in.}$) rigid cracking frame specimens were used to determine the stress at cracking. Lognormal fits of the cracking stress from 64 cracking frame tests and the tensile strength calculated from the measured compressive strength using three commonly used equations based on compressive strength were developed.

The main cause of degradation for reinforced concrete (RC) structures is the corrosion of the steel reinforcement. Laboratory tests aimed at studying durability are typically accelerated to provide usable results within a reasonable period of time, and well-established electrochemical techniques are used for the assessment of corrosion. However, because these techniques are not suitable for continuous monitoring and are often intrusive, nondestructive testing (NDT) techniques are also suitable for monitoring. Acoustic emission (AE) is one of the NDT techniques used to detect the onset and progression of corrosion. This paper presents an accelerated corrosion test setup and AE monitoring methodology based on the historic index, $H(t)$, for laboratory experiments on RC specimens. Accelerated corrosion is attained by increasing the capillarity suction of RC exposed to chlorides. The frequency spectrum of the AE signals before and after the initiation of corrosion is investigated to isolate the frequency components associated with corrosion. It is shown that the AE signals generated by early corrosion excite a well-defined narrow band of the frequency spectrum.

Buildings made of brick count for a large portion of Austrian buildings. For these masonry buildings, the compound between mortar and brick is essential. This study analyzes the fracture mechanical properties of mortar-brick compounds. A wedge splitting method is used to evaluate the notch tensile strength as well as the specific fracture energy. On the one hand, mortars with different compressive strengths are used. On the other hand, the surface of the bricks is modified during the study. It can be shown that bricks with grooves have a better compound and that the quality of the compound depends on the relation of groove depth to maximum grain size of the mortar.

This paper presents a study on the shear load-displacement behavior of horizontal joints in unreinforced brick masonry subjected to constant compression. In general, under static shear loading masonry joints show a peak shear stress followed by a residual shear strength. To investigate these aspects in greater detail, triplet tests were conducted on masonry specimens using different types of mortar. The results found in this study and previous tests show that normal compressive stresses acting on the interface and the interface mortar strength affect the peak shear stress and the residual strength in a rather similar way. The cohesion and the internal friction angle, i.e., the two parameters required by the Mohr-Coulomb criterion, are then derived from a linear regression of the test results. The pre-peak and post-peak response of a masonry bed joint can best be represented by simple equations, and their shear stiffness depends on material properties and the magnitude of the normal compression. Computational modeling strategies are then presented considering the shear slip at the brick-mortar interface. The comparison of the model prediction with the results found in this study and previous tests shows the reliability of the proposed model for bed joint behavior.

To address the ever-increasing quantity of scrap tires produced in the United States, a study is conducted on the use of crumb rubber in concrete for use in structures against near-field blast and ballistic demands. Crumb rubber concrete (CRC) is produced by replacing a volume percentage of the traditional coarse and/or fine aggregate with crumb rubber particles. Crumb rubber is produced in various gradations from used vehicle tires through a variety of shredding processes. The influence of crumb rubber on the constitutive and structural performance of concrete under quasi-static loading has been examined in past research. CRC has been shown to have decreased strength and stiffness while still being a useable structural material. This research study examines the use of CRC for the specialized application of blast and ballistic protection. The program characterizes resistance of CRC to contact and near-contact high explosive detonations, and examines depth of penetration, and perforation using V50 methods. The results of the experimental and analytical investigation found that (1) the addition of crumb rubber results in decreased resistance to ballistic demands and near-field blast loads, (2) the reduction is less than that estimated by accepted predictor methods, and (3) when normalized by weight rather than thickness, the use of CRC results in an improvement in resistance to ballistic and near-field blast demands.

Asphalt concrete (AC) consists of approximately 95% aggregate, by weight. Of this 95%, about 6% is smaller than 0.075 mm in size (passing the #200 sieve and called filler). The fillers often contain mica, which is a formation of silicate minerals having perfect basal cleavage. Mica has been shown to reduce the strength of AC. This study evaluates the effects of mica on asphalt materials subjected to aging. Mica is combined with asphalt binders to make mastics. Mastics are aged at four different levels and tested by nanoindentation to determine modulus and hardness values. It is shown that mastic with no mica becomes much harder after long-term aging. Aged mastic with no mica is shown to be harder than the aged mastics with low concentrations of mica. Mastic with less than 5% mica in the fillers behaves similarly to binder. However, with a mica content of 7.5%, the modulus decreases after long-term aging. A mastic sample containing 5% mica is shown to have the highest modulus value. Therefore, low-concentration mica reduces hardness but increases modulus value of aged mastic. Therefore, mica can be used to control long-term aging behavior of asphalt concrete.

The aim of this study is to investigate the effects of field-compaction conditions on the mechanical properties of asphalt concrete and then compare the properties with those of the specimens prepared with different Marshall hammer–blow numbers and gyratory-compactor gyrations. For this purpose, a binder layer was constructed with different compaction levels at different temperatures over a preconstructed plant-mix base layer. The B 70/100 bitumen and dense-graded limestone aggregate with a maximum size of 25.4 mm were used. The binder layer was divided into 12 sections, which were constructed with four different road roller–pass numbers and three different temperatures. The laboratory compaction conditions simulating all of the field compactions were assessed in indirect tensile strength, indirect tensile stiffness modulus, indirect tensile repeated load, and dynamic-creep tests. It was concluded that the field and laboratory specimens were affected by the compaction level and temperature in different ways. Furthermore, they exhibited different performances even with the same air-void contents. The laboratory specimens with the same air-void contents as those of field specimens displayed much better performance than the field specimens.

This paper presents a study in which the feasibility of utilizing two industrial wastes, a heavy clay material from the automotive industry and a waste foundry sand from the metallurgical industry, as construction materials was evaluated through laboratory experiments. The laboratory study blended two industrial wastes at different proportions and stabilized the blend with varying amounts of cement. The engineering properties of the blends were evaluated through the Atterberg limits, Proctor compaction test, direct shear, and unconfined compressive strength tests. The results from this study indicate that blending foundry sand into waste heavy clay significantly reduced its plasticity and cohesion and hence made it possible to be further stabilized with cement. In addition, it is observed that the blended materials had other improved properties such as increased maximum dry unit weight, friction angle, and compressive strength. However, the increase in compaction and strength properties became less significant with the increase of foundry sand content. An optimum blending ratio was recommended through this laboratory study.

This paper studies the effect of rice husk ash (RHA) in the properties of hydrated lime (calcium lime-CL90s) mortars with a view to improve their properties and make them more sustainable. The variation in mortar properties was related to the activity of the RHA, which was assessed by measuring its specific surface area, fineness, reactivity, composition, and amorphousness. According to the results, the RHA investigated is a low-temperature, highly reactive ash of high specific surface area that contains crystalline silica and unburnt cellulosic material and was probably produced between 400 and 500°C. Pozzolanic hydrates were clearly present after 24 h, progressively increasing in size and amount (at 3 and 7 days) and linking to each other to form continuous networks after 14 days. The paper concludes that lime replacement by RHA improves mortar workability, lowering water/binder ratio and the amount of water required to reach a specific consistency. RHA also enhances bulk density and lowers the difference between real and bulk densities thus resulting in lower porosity. Lime replacement by RHA enhances strength, and accelerates setting and early strength gain. Finally, with increasing RHA content, lime mortars become progressively stiffer and more elastic, yet remain plastic and thus undergo significant strain before failure.

Fatigue tests were conducted on natural corrosion deformed bars. The specimens were taken from a temporarily halted construction project. A method of mass loss was adopted in this study. High-cycle low-amplitude fatigue tests were performed to failure using five levels of cyclical stress range. The fatigue life of medium-corrosion deformed bars reduces sharply compared to that of noncorrosion ones. The failure mechanism in fatigue is examined by using a scanning electron microscope (SEM). Results indicate that the loss in fatigue life comes at the expense of the number of cycles needed to initiate fatigue cracks and is attributed to pitting corrosion.