Journal of Materials in Civil Engineering

Local recycling pressures are providing an impetus to examine the use of unconventional materials in construction such as waste glass in Portland cement concrete. It is well known that the silica in glass can be highly reactive with the alkalis in cement paste and that this reaction can lead to expansion and cracking of the concrete (alkali-silica reaction or ASR). The potential is examined for controlling ASR and achieving concrete of suitable strength and durability that uses waste glass as the aggregate. Laboratory and field research have been completed with concrete mixtures designed primarily for paving or flat-work applications. Various gradations of glass particle sizes added at various fractions of total aggregate content have been studied. Compressive strength and wet prism expansion are two of the parameters monitored. The study has spanned several years and has revealed both glass aggregate concrete mixtures that show great promise as well as mixtures that fail rapidly. Continued monitoring of the performance of the successful mixes over a period of several more years will provide an important step toward defining those situations where waste glass can be used in concrete.

Chloride transport in concrete is often subject to an electric field. This may arise from an internal source, such as the development of a membrane potential, or it may be imposed on the concrete by an external source, as is often the case when electrochemical remediation techniques are applied and accelerated chloride diffusion tests are undertaken. In this work the theory of chloride migration and its practical applications are reviewed. The migration of ions in an electric field differs from other transport processes in that positive and negative ions move in opposite directions, and the condition of electroneutrality does not impose the same constraint on the transport of ions as would otherwise be the case. Well established laws with appropriate boundary conditions have been used to model chloride transport in concrete under electrochemical chloride extraction and cathodic protection conditions, as well as in accelerated chloride diffusion tests. The minimum electric field that will prevent further chloride contamination may be regarded as the threshold requirement for chloride removal and also provides a basis for a corrosion prevention measure in its own right. The quantification of the membrane effects of concrete on the transport of chloride ions and the time dependence of chloride binding and dissolution require further research.

In-place test methods are available that can be used as alternatives to testing field-cured specimens to evaluate concrete strength in a structure. However, in-place test results do not represent the compressive strength of concrete directly but are empirically correlated to the compressive strength. Therefore, to use in-place test methods to estimate the strength of concrete, a preestablished relationship is required between the in-place test results and standard cylinder test results. In addition, a statistically based procedure is needed for a reliable estimate of concrete strength based on the strength relationship and in-place test results. This paper describes the statistical framework for developing the strength relationship and provides a step-by-step procedure to evaluate the characteristic compressive strength of concrete from in-place test results. Pullout test data are used to illustrate the use of these computational procedures.

Bridge material selection is one of the most difficult decisions an engineer has to make. Many factors and individuals are often involved in choosing the proper bridge material for a given site and location. Physical factors such as strength and lifespan of material, and also site specific factors like roadway alignment and traffic count, play important roles in material selection. Often state Department of Transportation engineers, private consulting engineers, and local highway officials all play roles in the material selection process. Each individual may have his/her own perception of bridge materials based upon past experience and education, and little is known about how these perceptions influence the choice of materials. In this study, perceptions of engineers and highway officials toward timber as a bridge material in four selected states were compared to the actual performance of timber as reported in the National Bridge Inventory. Highway officials and engineers in Mississippi, Virginia, Washington, and Wisconsin were surveyed by mail and personally interviewed to capture their perceptions toward timber as it compared to other major bridge materials (prestressed concrete, steel, and reinforced concrete). This information was compared with the actual performance data obtained from the National Bridge Inventory. The results indicate that there is a strong correlation between highway officials' perceptions toward bridge materials and the reported performance of these materials.

In this study the properties of self-flowing concrete, in which flow was >600 mm, containing fly ash were experimentally investigated and compared with those of ordinary concrete. For five types of self-flowing concrete mixtures and three types of ordinary concrete mixtures several tests, such as flow test, slump test, O-funnel test, box test, L type test, and setting time test, were carried out to obtain the properties for flowability and workability of fresh concrete. The mechanical properties of hardened concrete were also investigated in terms of compressive strength, splitting tensile strength, modulus of elasticity, stress-strain relation, creep, and drying shrinkage. In fresh concrete it was found that self-flowing concrete had excellent workability and flowability compared to ordinary concrete, and volume ratio of coarse aggregate-to-concrete greatly influenced flowability and workability. Self-flowing concrete also had good mechanical properties at both early and late ages with compressive strength reaching as high as 40 MPa at 28 days. The creep of self-flowing concrete investigated was greater than that of ordinary concrete at early ages, and drying shrinkage was much higher.

Application practices of bituminous hot-poured crack sealants, typically used to effect repairs on pavements, were monitored in the field and heating conditions were reproduced in the laboratory. From viscometry, thermogravimetry, and tensile testing measurements, it was found that sealants degrade upon heating at recommended installation temperatures. Consequently, given the level of product degradation observed from laboratory evaluations, it is not expected that a consistent low temperature sealant performance could be obtained in the field. These conclusions help explain the number of premature sealant failures that exist despite the fact that these materials may be in accordance with the requirements in ASTM D 3405.

This paper is intended to verify the concern expressed by researchers that stiff asphalt-mineral filler mastics may lead to the cracking of flexible pavements in the brittle-ductile region. Test results obtained from the direct tensile test show that both tensile stress and tensile strain increase with increasing mineral fillers. The failure energy of asphalt-mineral filler mastics also increases with filler concentration because of increases in strength and strain. With increasing tensile strength, it is implied that there is a good adhesion between asphalt binders and mineral fillers. The tensile strength of asphalt-mineral filler mastics decreases as the size of filler particles increases. However, at very low temperatures plain asphalts and mastics exhibit low strains, indicating that mineral fillers may not be the cause of cracking. Interaction mechanisms between mineral fillers and asphalt binders are proposed to explain the increase of stress and strain. After reviewing various composite models, a particulate-filled composite model is selected to accurately predict the tensile strength of asphalt-mineral filler mastics.

In this paper, a novel neural network architecture, augment-neuron network, is proposed and examined for its efficiency and accuracy in modeling concrete strength with seven factors (water/cement ratio, water, cement, fine aggregate, coarse aggregate, maximum grain size, and age of testing). The architecture of the augment-neuron network is that of a standard back-propagation neural network, but augment neurons, i.e., logarithm neurons and exponent neurons, are added to the input layer and the output layer of the network. Two hundred examples were collected from actual experimental data from 15 sources. The system was trained based on 100 training examples chosen randomly from the example set, and then tested using the remaining 100 examples. The results showed that the logarithm neurons and exponent neurons in the network provide an enhanced network architecture to improve performance of these networks for modeling concrete strength significantly. A neural network–based concrete mix optimization methodology is proposed and is verified to be a promising tool for mix optimization.

Current distress analysis practices and material specifications associated with low temperatures, including recent developments by the Strategic Highway Research Program, do not address the potential for localized damage associated with thermal incompatibility of asphalt concrete components. The analytical approach used to explain transverse surface cracking assumes a homogeneous pavement material. Although this approach produced satisfactory results for the prediction of low temperature cracking, it may obscure other forms of damage related to exposure to extreme low temperatures. This paper discusses localized forms of damage related to the vast difference in the coefficients of thermal contraction of asphalt concrete components (binders and mineral aggregates). Microscopic examination of asphalt concrete samples exposed to low temperatures revealed the presence of hairline cracks within the asphalt matrix. The examination also revealed deterioration of the bond at the aggregate/binder interface. The observed damage patterns explain the results of mechanical testing conducted using indirect tensile strength and three point bending procedure. Analysis demonstrates the potential impact of the observed forms of damage on pavement performance. It also explains results published by other researchers.

Concrete or mortar has three phases, namely, aggregate, bulk paste, and the transition zone. The transition zone is the weakest link in the composite system; its presence may considerably affect the overall elastic moduli and the stress distributions in a concrete material. The transition zone has a relatively more porous structure compared with that of bulk paste, and it may not be perfectly bonded to the aggregate. This paper proposes a four-phase composite model for investigating the elastic stress analysis of concrete materials. The analytical solutions of a four-phase composite model subjected to uniaxial compression are presented in two dimensions (2D) and three dimensions (3D). Modeling of imperfect shear interfacial bond in a four phase composite model is shown. The 3D and 2D uniaxial compression solutions are compared. The effect of an imperfect shear interfacial bond on the elastic moduli and stress solutions is illustrated. A parametric study is carried out to study the sensitivity of the stress distributions in the transition zone due to different aggregate types and due to changes in the elastic moduli of the transition zone. It is shown that the elastic moduli of the transition zone and its interfacial shear bond with the aggregate could considerably affect the overall elastic moduli and stress distributions in a cement composite.