Journal of Materials in Civil Engineering

The weak mechanical properties of wood in tension perpendicular to the grain are often the origin of catastrophic brittle failure. In order to enhance the tension strength perpendicular to the grain and achieve a more ductile failure, flax fiber and glass fiber-reinforced polymer (FRP) composites were used to strengthen glue-laminated (glulam) timber specimens. Three series of specimen of glulam timber (flax fiber reinforced, glass fiber reinforced, and unreinforced), with a grand total of 28 specimens, were tested in tension perpendicular to the grain. For an approximate amount of FRP reinforcement of 1.2% in volume (thickness of $\sim 0.7\text{mm}$ ), an increase of the tensile strength of up to 74% was shown, with a stiffness increase of up to 41%. For all reinforced specimens, semiductile failures were observed. A parametric study was carried out using both the Monte Carlo (MC) method and the first-order second moment (FOSM) method. It is shown that the mean values obtained during experiments are in agreement with those from the MC simulation. However, the standard deviations from the MC simulation are larger. From the FOSM analysis, it is demonstrated that the variation in glulam stiffness perpendicular to the grain is not the first parameter driving the variation for the reinforced system. The variation in mechanical properties of the flax fibers appeared to be the driving parameter for the strength of the system.

Three-point bending tests on high-strength concrete specimens after exposure to high temperatures are presented, with a detailed evaluation of process zone size. The variables considered for the high-strength concrete were the types of fiber reinforcement: steel microfibers, polypropylene microfibers, and a hybrid combination of steel and polypropylene microfibers. Both virgin (no heat related damage) and heat treated specimens were tested by conducting experiments at ambient conditions approximately one month after exposure to the high temperature. For both undamaged and heat treated specimens, acoustic emission monitoring and high-resolution interferometric measurements were used to characterize the evolution of the finite size of the process zone as a function of the applied load. The size and shape of the localized damage zone due to prepeak microcracking are two of the significant factors influencing the strength of quasibrittle materials, i.e., the structural scaling. This paper reveals that the material ductility increases with the thermal damage, which is explained by the increase in the fracture process zone size. As a consequence, a correct interpretation of the experimental data requires an identification of fracture parameters through indirect methods.

Asphalt mixtures have two healing mechanisms: adhesive healing at the asphalt-aggregate interface and cohesive healing within asphalt binders. This study investigates the effects of cohesive healing exclusively, without considering the interaction of aggregates. This study also introduces a methodology of quantifying healing using the dissipated energy approach and the dynamic shear rheometer test with a specifically designed intermittent loading sequence. The ratio of dissipated energy change approach, which is based on the fundamental concept of dissipated energy and has been successfully applied to study hot mix asphalt (HMA) mixture healing, is applied to the binder. By doing so, a healing rate, defined as the rate of dissipated energy recovery per unit of rest time, is used to quantify the healing potential of asphalt binders. The results indicate that binder type, strain level, and temperatures have important impact on healing. It is recommended that the research methods introduced in this study be further applied to asphalt mastics and sand asphalt mixes to study adhesive and cohesive healing in HMA mixtures and provide fatigue-healing information for pavement design.

The aim of this investigation is to establish the correlation between concrete porosity, compressive mechanical strength, and microstructure using the results of nondestructive testing methods, i.e., ultrasonic pulse velocity (UPV) and image analysis. Researchers and engineers usually use results of standard laboratory procedures in order to obtain mechanical properties of a material. That process is long and it requires large number of samples, i.e., a lot of time and lot of material. Image Pro Plus (IPP) and UPV are methods which can provide equally accurate results. These methods are much more simple, rapid, and cheaper. Nondestructive test methods were applied on the corundum and bauxite based refractory concretes. Investigated concretes are varying in chemical and mineralogical composition. Mechanical compressive strength of concrete samples after thermal treatment at various temperatures (110, 800, 1,000, 1,300, and $1,500°\text{C}$ ) was investigated using standard laboratory procedure and afterward with UPV technique. Loss of strength and degradation occurs when refractory concrete sample is subjected to increased temperature and compressive load; therefore, measurement of mechanical properties can indicate and monitor the changes in the microstructure. Level of surface deterioration after thermal treatment was determined using optical microscope and IPP. Nondestructive ultrasonic measurement was also used as a means of monitoring of increasing porosity in refractory specimens. UPV technique and image analysis are reliable nondestructive methods for characterization of microstructural defects and can be useful when type of refractory concrete is to be chosen for an application.

Durability-related problem of any structure is a very important issue that cannot be overlooked, particularly for the structures located in coastal regions. In the coastal region the deterioration of structures often occurs due to aging, chloride ingress, etc., but the actions of living organisms are often underestimated. So a proper design of new structures and maintenance of old structures are essential since deterioration causes not only fatality but also economic burden to mankind. This paper focuses on the biodeterioration of coastal structures by marine algae (especially marine chlorophyceae Chaetomorpha antennina). To know its effect, the basic mechanism by which Chaetomorpha antennina deteriorates concrete structures has been highlighted. To ascertain the detrimental effect by marine algae Chaetomorpha antennina on coastal concrete structures, M20 grade concrete cubes were casted and kept in the coastal area where there is abundant growth of Chaetomorpha antennina. To examine the extent of deterioration done by Chaetomorpha antennina on concrete surface, samples were collected from the M20 grade concrete cubes kept in the coastal area. The collected samples were analyzed by scanning electron microscopy, energy-dispersive x ray, and x-ray diffraction to establish the degree of deterioration done by marine algae on concrete surface. The result showed that there is sustainable effect by the marine algae on the concrete surface.

Although concrete is widely considered a very durable material, if conditions are such, it can be vulnerable to deterioration and early distress development. Alkali-silica reaction (ASR) is a major durability problem in concrete structures. The product of this reaction is a gel that is hygroscopic in nature. When the gel absorbs moisture, it swells leading to tensile stresses in concrete. When those stresses coming from the gel swelling exceed the tensile strength of concrete, cracks occur. This paper is part of a broader research study to assist engineers to effectively mitigate ASR in concrete, leading to an increase in the life span of concrete structures. To achieve this objective, a comprehensive study on different types of aggregates of different reactivity was conducted to formulate a robust approach that takes into account the factors affecting ASR, such as temperature, moisture, calcium concentration, and alkalinity. A kinetic model was proposed to determine aggregate ASR characteristics which were calculated using the system identification method. Analysis of the results validates that ASR is a thermally activated process and, therefore, the reactivity of an aggregate can be characterized in terms of its activation energy $\left(E_a\right)$ using the Arrhenius equation.

Electromagnetic sensors can be exploited to determine properties (i.e., density) of hot mix asphalts (HMAs) by observing the surface polarization effects that occur in the radio frequency range of the electromagnetic spectrum. A challenge is the modeling of electromagnetic sensors, which do not require penetrating probes to perform the measurement. Moreover, core extraction is time consuming and subjected to technical and operator errors. In this paper, in order to model an electromagnetic sensor for HMA density measurement, a finite element code modeling a particular case of study has been exploited. A subsequent objective has been to determine HMA electrical characteristics and their relation with density values obtained with a nonnuclear device evaluating in-place HMA pavement. An experimental plan has been designed. The obtained results demonstrate that the implemented model is able to explain the relationship between density and electrical properties of HMA layers. Practical applications and recommendation have been outlined.

Fifteen hwangtoh-based alkali-activated concrete mixes were tested to explore the significance and limitations of the development of cementless concrete without carbon dioxide emissions while maintaining various beneficial effects. Hwangtoh, which is a kind of kaolin, was incorporated with inorganic materials, such as calcium hydroxide, to produce a cementless binder. The main variables investigated were the water-binder ratio and fine aggregate–total aggregate ratio to ascertain the reliable mixing design of hwangtoh-based cementless concrete. The variation of slump with elapsed time was recorded in fresh concrete specimens. Mechanical properties of hardened concrete were also measured, including compressive strength gain, splitting tensile strength, moduli of rupture and elasticity, stress-strain relationship, and bond resistance. In addition, mechanical properties of hwangtoh-based cementless concrete were compared with those of ordinary portland cement (OPC) concrete and predictions obtained from the design equations specified in American Concrete Institute 318-05 and Comite Euro-International du Beton-Federation International de la Precontrainte for OPC concrete, wherever possible. Test results show that the mechanical properties of hwangtoh-based concrete were significantly influenced by the water-binder ratio and to less extend by fine aggregate–total aggregate ratio. Based on the measured mechanical properties and code provisions, it can be proposed that the hwangtoh-based alkali-activated concrete is practically applicable as structural concrete when the water-binder ratio is less than 40%.

Some authors argue that new binders are needed to replace ordinary portland cement (OPC) for enhanced environmental and durability performance. Alkali-activated binders have emerged as an alternative to OPC binders, which seem to have superior durability and environmental impact. This paper report results of a research project on the development of alkali-activated binders using waste mud from a tungsten mine. Abrasion and acid resistance of two ordinary portland cement (OPC) strength class concrete mixtures (C20/25 and C30/37) and several tungsten mine waste mud (TMWM) mixtures were evaluated. Acid resistance was performed by submitting samples to solutions of sulfuric acid, nitric acid, and hydrochloric acid, results of weight loss are reported. Abrasion resistance was assessed by the mass loss of cubic specimens when submitted to 1,000 rotations with the Los Angeles apparatus test machine. This study indicates that TMWM binders possess higher acid and abrasion resistance than OPC based concrete mixtures. The environmental assessment of the TMWM binders shows it can be considered an inert material which indicates that it could be used as a building material.

In the production of self-consolidating concrete (SCC), long hauling times are often necessary for transportation to the job site. During such hauling time, highly fluid SCC can lose a significant amount of slump flow, necessitating the mixtures to be remediated. Consequently, hauling and remediation can have a detrimental effect on the air void size and spacing, which are necessary characteristics for guaranteeing adequate frost durability in the hardened concrete. The purpose of this investigation was to determine the effects of two forms of remediation, overdosing and retempering, on the air void characteristics of SCC. Three slump flows of 559, 635, and 711 mm and eight hauling times from 20 to 90 min were studied. The required admixture dosage for each remediation technique depended on the target slump flow and hauling time duration. Hauling time and remediation caused the air content to increase and air void characteristics to improve from their initial state, although they typically were inferior to the nonremediated mixtures. Both forms of remediation exhibited similar trends in air void characteristics with hauling time.

This paper presents the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX. This tunnel was originally founded on a limestone material. Distress locations were identified where possible delamination of shotcrete layer and moisture leaks were either suspected or noticed. As a part of the research, rock cores and white powderlike substance behind the liner were collected around the distressed locations, and these cores and powder material were subjected to chemical, mineralogical, and engineering tests to understand the potential causes of this distress. Mineralogical tests, in particular, X-ray powder diffraction analysis on a powder material and gel-like substances collected on the liner, showed the presence of anhydrite, gypsum, and ettringite traces. High amounts of sulfate measurements in chemical and energy dispersive X-ray spectroscopy studies also showed that both gypsum and ettringite formations were possible in and around the limestone material. Upon hydration, mineral expansion of ettringite and anhydrite led to heaving and subsequent cracking of the adjacent shotcrete layer. Engineering characterization tests including unconfined compression strength (UCS), indirect tensile strength (ITS), and triaxial tests on rock cores embedded with a powder type sulfate material revealed that low strength cores were obtained near high distress zones and high strength cores were collected at low distress zones. The UCS values ranged from 6.2 (high distress) to 13.8 MPa (low distress) whereas the ITS values of the cores varied from 0.5 to 1.1 MPa for the same distress locations. This indicates the potential loss of strength of these rock materials from the presence of gypsum material in them. Possible methods to mitigate this heaving problem behind the liner are also discussed.

In the analysis or design process of reinforced concrete structures, the peak stress and strain in plain concrete under triaxial stress are critical. However, the nonlinear behavior of concrete under triaxial stresses is very complicated; modeling its behavior is therefore a complicated task. In the present study, several radial basis function neural network (RBFN) models have been developed for predicting peak stress and strain in plain concrete under triaxial stress. For the purpose of constructing the RBFN models, 56 records including normal- and high-strength concretes under triaxial loads were retrieved from literature for analysis. The $K$ -means clustering algorithm and the pseudoinverse technique were employed to train the network for extracting knowledge from training examples. Besides, the performance of the developed RBFN models was estimated by the method of three-way data splits and $K$ -fold cross-validation. On the other hand, a comparative study between the RBFN models and existing regression models was made. The results demonstrate the versatility of RBFN in constructing relationships among multiple variables of nonlinear behavior of concrete under triaxial stresses. Moreover, the results also show that the RBFN models provided better accuracy than the existing parametric models, both in terms of root-mean-square error and correlation coefficient.

This technical note proposes a simple analytical model for predicting the shear strength behavior of fiber-reinforced granular soils under high confining stresses, where it can be assumed that pullout of fibers does not take place. The model presents an analytical expression derived from the force-equilibrium consideration incorporating several significant parameters describing the characteristics of the granular soil and the fibers, such as fiber content, aspect ratio, modulus of elasticity of fibers, specific gravity of fiber material, soil-fiber friction, initial orientation with respect to shear plane, normal confining stress, specific gravity of soil particles, angle of shearing resistance of soil, and void ratio of soil. The expression shows that inclusion of fibers in the granular soil induces cohesion, may be called apparent cohesion, as well as increase in normal stress on the shear failure plane, which are proportional to the fiber content and aspect ratio, implying that increase in shear strength is also proportional to the fiber content and aspect ratio. The results based on this model are discussed for some specific range of parameters in their practical ranges. It is observed that the increase in shear strength of the granular soil due to the presence of fibers is significantly contributed by the apparent cohesion, and the contribution to the shear strength from the increase in normal stress is limited. The model shows that the increase in shear strength follows the trends of variation as reported in some previous works.

This paper addresses the potential use of granulated rubber as backfill material for buried pipelines in cold regions. An experiment on a laboratory scale buried pipe was conducted to evaluate the pipe-backfill interaction upon freezing. Two backfill materials were employed. In Case 1, sand was used as backfill material. In Case 2, granulated rubber was mixed with sand. Induced circumferential and longitudinal strains along the pipe were measured with movement of the freezing front into the backfill and an estimate of the freezing soil pressure was obtained based on the measured pipe strain. Experimental results showed that the behavior of the buried pipe was influenced by the progression of the freezing front and type of backfill material. Cold temperatures advanced faster into the sand backfill compared to the rubber-sand backfill due to the good thermal characteristics of rubber. Circumferential strains increased in both backfills indicating the development of freezing soil pressure in the backfill. Dominant vertical compressive strains were observed at 0° and 180° in both backfills. A significant reduction in strain and pressure exerted on the pipe upon freezing in the rubber-sand backfill was confirmed and the application of rubber mixed with sand as backfill material is possible.