Journal of Materials in Civil Engineering

The temperature profiles in a hydrating concrete slab are produced by a two-dimensional finite-element method software tool, ${\mathrm{TMAC}}^2$ (temperature and moisture analysis for curing concrete), as a function of time and ambient boundary conditions described in this paper. To include the effect of the heat of vaporization, heat flux due to evaporation is included in the boundary condition of heat transfer at the slab surface in addition to the effects of surface humidity, effective curing thickness, and surface moisture emissivity on the rate of evaporation. Thermal conductivity is back-calculated using the data collected from laboratory measurements toward the improvement of the modeling of thermal conductivity. Theoretically, the material properties determined in this manner should facilitate accurate temperature prediction. Thus, temperature prediction in hardening concrete pavements under various conditions can be effectively calibrated by improved material characterization. To this end, this paper provides the basis of a calibration protocol.

This paper describes an experimental investigation to assess the development of the localized damage zone in concrete tested in compression. Cylindrical specimens were loaded and unloaded at different maximum strain levels. The mechanical response was measured and compared with acoustic emission activity. As expected, the acoustic emission activity increased with an increase in load. To establish a correlation between mechanical damage and acoustic emission activity, the acoustic emission events were categorized on the basis of their amplitude and duration. Higher amplitude and longer duration events occurred in the specimens at higher damage levels. A linear correlation was observed between the mechanical fracture energy and the measured acoustic emission energy. Triangulation was used to locate the position of the acoustic emission events and to assess the development of the damage zone during testing. The compression damage zone (CDZ) was found to develop at the time of peak stress with a length of approximately 1.2 times the diameter of the specimen. The size of the CDZ was observed to increase to double the diameter of the specimen at 1.6 times the strain at peak. While preliminary, these results indicate how the damage develops to form a zone that influences the stiffness degradation and the postpeak response of the concrete.

Structural design relies essentially on tests made on cylinders of small size to estimate the probability of failure of prototype members, since full-scale testing of structures to determine their strength is not feasible. The confidence that such scale modeling deserves in terms of representation of actual behavior needs careful examination, due to such factors as material nonlinearities, difficulties of scale representation of particulate materials, and sometimes the impossibility of simultaneously satisfying independent dimensionless parameters. Some failures explained by linear fracture mechanics are associable with strong size effects, as opposed to the cases where small cracks are a material property. Besides research centered on these problems, a number of studies of scale effects have been associated with the increased probability of finding a flaw in larger objects. In fact, geometric similitude may coexist with microscopic randomness of flaws that cause size effects to appear. The type of material of the object under study may also be a decisive factor. For example, scatter of the mechanical properties in unidirectional fiber-reinforced polymers (FRPs) is much larger than in metals due to a larger density of flaws. Thus the strength of FRP laminates may depend on the volume of material involved. Strengthening reinforced concrete columns with FRP wraps leads to new constitutive laws for the overall response of the columns and requires small-scale testing followed by extrapolation for design use. The present paper focuses on the difficulties of this step, based on the experimental data obtained. The questions mentioned above are addressed, and the relevance of the adequate representation of the lateral stiffness of the FRP jacket in the scaled cylinders is emphasized. The paper also addresses the problem of testing confined cylinders with a given slenderness ratio $H∕D=\text{height}∕\text{diameter}$ , within the range usually characteristic of short columns, and extrapolating the results for columns of different $H∕D$ . The importance of the parameter (thickness of jacket/diameter of column, representative of stiffness of jacket/stiffness of concrete core) is also examined. The influence of the parameter is shown to be relatively minor, whereas the nonscaling of the relative stiffness of the core and jacket would be a major cause of error. The experimental data, in terms of strain and strength, are also compared with numerical models proposed in the literature, and the quality of the approximations is analyzed.

Deleterious damage that manifests in cracking and strength loss due to expansion and exfoliation often occurs when hardened concrete is exposed to sulfates. For a degradation-free service life, modeling sulfate attack is as important as considerations for strength and stability in concrete. This paper focuses on modeling the impact of gypsum as a constitutive durability product responsible for strength loss in concrete due to sulfate attack. The model blends the calculation of coupled moisture-sulfate transport processes with quantitative simulation of chemical reactions involving sulfates, moisture, and an incipient portlandite phase in concrete. Account is taken of variations in sulfate and moisture diffusivities to reflect microstructural changes when a portlandite matrix is stoichiometrically transformed to gypsum. Implementation of the model to both water-saturated and unsaturated concretes is numerically achieved according to standard Galerkin procedure in the finite-element sense. Contrary to expectations, simulation results for the case of initially unsaturated specimens before immersion in a sulfate solution are not significantly different from the initially saturated condition. Calculations of global relative residual strength predicated on degradation profiles generated by the model showed good agreement with postsulfate-immersion-test residual strength data.

The strain-sensing ability of carbon fiber cement, as based on piezoresistivity, remains in the presence of damage, although the gauge factor (fractional change in resistance per unit strain) is affected by strain and damage. The longitudinal gauge factor is diminished by compressive strain by up to 70% and by damage by up to 25%. The magnitude of the transverse gauge factor is diminished by strain by up to 60% and by up to 25% by minor damage not accompanied by irreversible strain, but it is increased by up to 120% by major damage accompanied by irreversible strain. The gauge factor, whether longitudinal or transverse, is reduced in magnitude as the specimen size increases (by $13\text{to}51\mathrm{mm}$ ).

This paper presents some of the most interesting steps followed by the Canadian team from Laval University in developing a high tensile strength, lightweight concrete for the construction of their canoe. This mixture was used in 2004 by the Laval University Concrete Canoe Team, which, year after year, participates in an engineering challenge. The objective is to develop a concrete mixture that can be pumped and shot on a male mold using a custom shotcrete technique. The 2004 mix contains acetone to enhance its fluidity and Welan gum to increase its viscosity, thus preventing segregation.

Considerable efforts are being taken worldwide to utilize local natural waste and by-product materials in making concrete, such as silica fume (SF) or rice husk ash (RHA) as supplementary cementing materials to improve concrete properties (durability, strength, etc.). The effect of using SF or RHA as a partial replacement for cement has been investigated. Ilmenite and baryte were used as heavy aggregates while gravel was used as a reference normal aggregate. Physical, mechanical, and shielding properties of different types of heavy weight concrete were studied. The durability of the studied concrete was investigated. The study was extended to investigate the microstructure, the infrared and thermal analysis, and the effect of absorbed gamma radiation of the studied concrete types. Results showed that ilmenite concrete mixed with 15% SF had the highest density; compressive, tensile, flexural, and bond strengths; modulus of elasticity; and attenuation coefficient values. Concrete mixed with RHA had good resistance to sulfate attack, while concrete mixed with SF had better resistance to sulfate attack. There was no significant effect for either SF or RHA on the concrete gamma attenuation coefficient. Results showed that concrete mixed with RHA had higher mechanical and physical properties than that mixed without any additives but lower properties than that mixed with SF.

This research was conducted to understand the effects of curing compounds and their application methods on concrete properties. In the research, three different curing compounds were selected and applied to lab and field concrete at different times. The curing compounds were applied with two methods—single- and double-layer sprays. Moisture content, electrical conductivity, sorptivity, and strength tests were performed to investigate the effects of curing on concrete properties, especially on the near-surface layer concrete properties. The experimental results indicated that for pavement without curing compound, the properties of the near-surface layer were considerably different from those of the internal layers. By decreasing the differences between the layers through proper curing technique, a pavement would have more uniform properties throughout its depth. Based on the results, the test methods for quantifying concrete curing effectiveness were also evaluated.

The study presented in this paper deals with the fire performance of balsa sandwich panels made using inorganic Geopolymer resin and high-strength fiber facings. A thin layer of a fire-resistant paste composed of Geopolymer and hollow glass microspheres was applied to the facings to serve as a protective fire barrier and to improve the fire resistance of the sandwich panels. Using 17 sandwich panel specimens, the primary objective of this program was to establish the minimum amount of fireproofing necessary to satisfy the Federal Aviation Administration (FAA) requirements for heat and smoke release. The influence of this fireproofing insulation on the increase in mass of the panels was also evaluated. The system is simple and inexpensive to manufacture, and a $1.8\text{-}\mathrm{mm}$ -thick layer of fireproofing satisfies the FAA requirements for both heat release and smoke emission.

This paper presents the result of an effort to characterize asphalt emulsions that are typically used in cold in-place recycling applications using the current specifications for asphalt binders. Four asphalt emulsions were investigated: CRS-2P, CSS-1, EE, and HFMS-2P. The emulsions were cured using two methods: (1) cure in air at room temperature (air-cured); and (2) use a modified rolling thin film oven test (RTFOT) approach (RTFOT-cured). The air-cured samples were also aged in the pressure aging vessel. The residues were tested using the bending beam rheometer (BBR) and the direct tension test at low temperatures and the dynamic shear rheometer at high and intermediate temperatures. The methods described in AASHTO M320 and MP1a specifications were used to determine the critical temperatures for the four asphalt emulsions and master curves of the absolute value of the complex modulus $\mid G^{*}\mid$ were obtained to investigate the rheological behavior of the residues.

Self-compacting concrete (SCC), a recent development, eliminates the need for internal or external vibration, as it freely flows in and around dense reinforcement and fills the mold completely without any blockages. SCC would be an ideal material for cast in situ piles, where compaction is infeasible. Six double under-reamed piles having a diameter of $250\mathrm{mm}$ and a length of $4\mathrm{m}$ , three made of SCC and three of conventionally vibrated cement concrete having similar strengths, were cast and tested to evaluate their static behavior in axial compression and tension (pullout). Later, all the piles were exhumed using suitable machinery to examine whether the pile shaft and bulbs had been well formed. Ultrasonic pulse velocity measurements were also taken on the exhumed piles along the length to evaluate the integrity of the concrete. Concrete cores of $75\mathrm{mm}$ diameter and $150\mathrm{mm}$ height taken from the pile shaft were tested for mechanical and durability related properties. The experimental study clearly demonstrated that the SCC in situ piles had better control on geometry when cast against soil form work.

Composite lintels are formed above the door and window openings of glass-fiber-reinforced gypsum (GFRG) wall constructions. These lintels are constructed by filling reinforced concrete into the hollow cores of the GFRG walls. The GFRG panel itself is a composite material composed of gypsum plaster and the reinforcing glass fiber. When filled with reinforced concrete the structural action of the lintels is derived from further composite action between the GFRG panel and the infill concrete. Experimental beam testing was conducted to study the flexural and shear behavior of these composite lintels. Typical failure modes and corresponding ultimate strengths were obtained and analyzed. Based on the test results, theoretical design models and guidelines are proposed for both the flexural and shear strengths.

In service, concrete can develop cracks or microcracks that can influence the transport of liquids and ions. This paper describes an investigation of fluid transport in concrete damaged by tensile loading or freeze–thaw cycling. Acoustic emission was used to quantify the extent of damage in the specimens exposed to tensile loading while resonant frequency was used to quantify the extent of damage in the specimens exposed to freezing and thawing. Water absorption was measured in the damaged concrete. The presence of freeze–thaw damage increased both the initial sorptivity and total water absorption. Electrical conductivity was measured and found to increase in a bilinear fashion with freeze–thaw damage. A knee point in the electrical conductivity versus freeze–thaw damage curve was observed when the dynamic modulus degraded to 75% of its initial value, which appears to correspond with the coalescence of cracking. Mechanical loading was found to only increase water absorption on a local level, but it did not substantially influence the overall water absorption.

Mechanical clinching was developed originally for the automotive industry. It is now starting to be used in the construction industry in the fabrication of cold-formed steel building systems. Effective, efficient, and reliable structural connections can be formed using the technique. The strength of mechanical clinching is affected by a number of factors including steel thickness and strength, direction of applied load, and the geometric configuration of the clinching tools. This paper summarizes the results of a large number of tests on mechanical clinching that formed part of a research program into the application of clinching in cold-formed steel structures. Different modes of failure occur in the two orthogonal directions of applied shear. Theoretical expressions are derived to predict the strength of mechanical clinching based on the two different failure modes. Good agreement with the experimental results is obtained. It is also shown that the strength of mechanical clinches subjected to shear applied at intermediate angles can be predicted reliably by linear interpolation between the strengths in each of the two orthogonal directions.

Extruded high-performance fiber-reinforced cementitious composites offer a number of benefits over the materials currently used in residential construction, including improved strength, ductility and durability, increased design flexibility, improved safety in the event of natural hazards, and greater affordability. However, nailing extruded materials using conventional methods is difficult. To be used in residential applications, the nailability must be improved so that these composites can be nailed in the same manner as conventional materials. Current test methods assess nailing performance using a static nailing load rate. However, because cementitious materials are rate sensitive, such static methods are not representative of actual field nailing. Therefore, a dynamic nailing test was developed that simulates field nailing. Using this newly developed test, the nailability of extruded composites was evaluated and compared with commercially available materials that are known to be nailable. The results indicate that extruded composites should be suitable for use in residential applications, but that slight material modifications are still needed to improve the nailing performance.

A high volume of lagoon (pond) ash produced as a waste from the thermal power station in India is used as a replacement of cement (55–65%) in concrete. The test specimens were prepared with and without superplasticizer. No air-entraining agent was used. At constant slump, the required amount of water reduced with the addition of lagoon ash. The slump retention property of the concrete with superplasticizer and lagoon ash was studied. A substantial increase in the setting time (initial and final) was observed. The development of early strength $(1,3\text{days})$ was low. The $28\text{-}\text{day}$ strength for concrete with lagoon ash, without the addition of superlasticizer, was in the range of $16.4–24.3\mathrm{MPa}$ for 65 and 55% cement replacement, respectively. The change in strength of concrete was observed over a period of $365\text{days}$ in the present study. The investigation shows a scope to utilize lagoon ash in concrete. An attempt was made to use lagoon ash in the concrete mix, referred as dry lean concrete, used as base course for concrete pavements.

Over the years, many methods have been developed to predict the concrete strength. In recent years, artificial neural networks (ANNs) have been applied to many civil engineering problems with some degree of success. In the present paper, ANN is used as an attempt to obtain more accurate concrete strength prediction based on parameters like concrete mix design, size and shape of specimen, curing technique and period, environmental conditions, etc. A total of 864 concrete specimens were cast for compressive strength measurement and verification through the ANN model. The back propagation-learning algorithm is employed to train the network for extracting knowledge from training examples. The predicted strengths found by employing ANN are compared with the actual values. The results indicate that ANN is a useful technique for predicting the concrete strength. Further, an effort to build an expert system for the problem is described in this paper. To overcome the bottleneck of intricate knowledge acquisition, an expert system is used as a mechanism to transfer engineering experience into usable knowledge through rule-based knowledge representation techniques.

This note outlines the experimental investigation of the factors affecting bond development between pavement layers. The tests involved the use of an apparatus known as the Nottingham shear box. To establish a realistic stress distribution at the interface, which would facilitate the analysis of the test results, finite element models of bonded and weakly bonded specimens were developed. It was concluded that care must be taken when interpreting test results from the shear box experiments. Several materials and four interface conditions were investigated. Bond stiffness and strength were assessed under repeated dynamic and monotonic static test conditions. The analysis of the experimental results showed that the interface properties depend more seriously on the type of materials in contact, rather than on the amount of the applied tack coat and the interface condition. It was suggested that the interface bond should be described by introducing a vertical shear reaction modulus, as well as using the horizontal shear reaction modulus.

Stabilized mud blocks (SMBs) are manufactured by compacting a wetted mixture of soil, sand, and stabilizer in a machine into a high-density block. Such blocks are used for the construction of load-bearing masonry. Cement soil mortar is commonly used for SMB masonry. This paper presents the results of an experimental investigation in characterizing the properties of SMB masonry using cement-soil mortars. The compressive strength, stress-strain relationships, and elastic properties of SMB masonry using three types of SMBs and cement-soil mortars are discussed. The influence of a cement-soil mortar’s composition and strength on masonry characteristics is examined. The results of masonry using cement-soil mortars are compared with those using conventional mortars (cement mortar and cement-lime mortar). Some of the major findings are: (1) SMB masonry strength is sensitive to block strength and increases with increase in block strength; (2) the strength of SMB masonry using cement-soil mortars is more sensitive to the cement content of the mortar than to the clay fraction of the mortar mix; (3) the masonry modulus increases as the block strength increases; and (4) SMB masonry with cement-soil mortars shows higher modulus than the masonry using cement mortar and cement-lime mortar.