Journal of Materials in Civil Engineering

An analytical model for the design of strain-hardening and multiple-cracking behavior of engineered cementitious composites (ECC) containing hybrid fibers is proposed. The model predicts first crack strength and ultimate bridging strength of hybrid fiber ECC. The model also predicts the minimum (critical) volume fraction of fibers required to exhibit strain-hardening and multiple-cracking behavior in uniaxial tension. The model is verified with the experimental results of hybrid fiber ECC specimens. A parametric study is also performed, using this model, to evaluate the effects of fiber length, diameter, and interfacial bond strength on the first crack strength, the ultimate bridging strength and the critical volume fraction of fibers. It is shown that the critical volume fraction of fibers in hybrid fiber composites can be optimized by proper selection of fiber length, diameter, and interfacial bond strength. Low modulus fibers are found to have a more pronounced effect on the strain-hardening and multiple-cracking behaviors of hybrid fiber composites compared to high modulus fibers. The hybrid fiber concept is found to offer additional freedom in the design variables compared to composite containing one type of fiber.

Geosynthetics have increasingly been used to reinforce many earth structures and are now a well-accepted means to improve engineering properties of various types of soil. However, most previous studies and applications of geosynthetic stabilization are confined to noncohesive soils. Few research efforts have been dedicated to the feasibility and benefits of geosynthetic reinforcement on cohesive soils. This paper presents the results of an extensive laboratory testing program using a large direct shear device, in which four different soils (including one sand and three clays of different plasticities) were reinforced by three different geogrids and one woven geotextile. Reinforcement mechanisms were analyzed and the soil–geosynthetic interface parameters were obtained from the testing results. The increase in molding moisture content and/or decrease in dry density caused an appreciable reduction in interface shear resistance, which suggests that it should be more rational to use interface parameters of soils at their 95% maximum dry density and moisture content 2% above their optimum values. This study also provides a basis for future research and modeling the behavior between cohesive soils and geosynthetics.

Proportioning of concrete mixes is carried out in accordance with specified code information, specifications, and past experiences. Typically, concrete mix companies use different mix designs that are used to establish tried and tested datasets. Thus, a model can be developed based on existing datasets to estimate the concrete strength of a given mix proportioning and avoid costly tests and adjustments. Inherent uncertainties encountered in the model can be handled with fuzzy based methods, which are capable of incorporating information obtained from expert knowledge and datasets. In this paper, the use of adaptive neuro-fuzzy inferencing system is proposed to train a fuzzy model and estimate concrete strength. The efficiency of the proposed method is verified using actual concrete mix proportioning datasets reported in the literature, and the corresponding coefficient of determination $r^2$ range from 0.970–0.999. Further, sensitivity analysis is carried out to highlight the impact of different mix constituents on the estimate concrete strength.

The effects of aggregate gradation, amount, and size on pervious portland cement concrete (PCC) static modulus of elasticity were compared using four different mixtures. A standard mix and three variable mixes using a uniform gradation, increased aggregate amount, and increased aggregate size were used. The effective air void content was determined for each mixture. The compressive strengths and static elastic moduli were determined and compared at equal void contents. For a uniform gradation, the compressive strengths and static elastic moduli appeared to be higher within an optimal range of voids; however, there was no statistically significant difference between the results from the different gradations. An increased aggregate amount resulted in a statistically significant decrease in both compressive strength and static elastic moduli due to the subsequent decrease in paste amount. While the compressive strengths were higher for mixtures containing smaller aggregate sizes, there was no significant difference between the static elastic moduli when different aggregate sizes were used. Further research is needed to understand the effects of aggregate size on the static modulus of elasticity of pervious PCC.

The maturity function provides a reliable approach in the determination of the in situ strength of concrete at later ages. This study was aimed at determining the strength–maturity relationship on concrete specimens which were prepared using different admixtures and cured under different temperatures. For this reason, three sets of concrete specimens, having dimensions of $15\times 15\times 15\mathrm{cm}$ , were produced using the set accelerating admixture, set retarding admixture, and no admixture content at a constant consistency and 0.59 water-to-cement ratio. All hardened concrete specimens were cured at 0, 20, and $40°\mathrm{C}$ temperatures under 100% humidity for 1, 3, 7, and $28\text{days}$ . The compression tests were applied on specimens at the end of the curing time. Equations for the relationship between maturity and strength were worked out for the admixtures used in the study.

This paper deals with the results of a study on the effect of curing on as-constructed smoothness and subsequent roughness development of portland cement concrete pavements (PCCP) in Kansas. Ten test sections on five newly built PCCP projects on I-70 and I-135 were selected. At each site, one section was cured with a double application of curing compound as opposed to the single application currently specified. A section of equal length with single application was designated as the control section. Some sections were instrumented with thermocouples to collect temperature data at the bottom of the PCCP slab during construction. Large temperature gradients between the top and the bottom of the PCCP slab were observed during concrete placement. Double curing compound application tends to decrease this temperature gradient. Periodic longitudinal profile data was collected with a South Dakota-type profiler on the wheel paths of both driving and passing lanes on each section. From these profile data international roughness index (IRI) statistics were computed for each test section. Analysis of variance was performed to compare mean IRI values with respect to the curing compound application rate. It was found that the single curing compound results in lower as-constructed IRI values, but double application reduces roughness development in the long run, possibly due to lower differential autogenous volume change of concrete.

Pipe-in-Pipe (PIP) configurations are considered as a practical solution to deepwater oil production to prevent hydrate formation and paraffin deposition during the transportation of crude oil to production facilities. The optimal design of a PIP configuration requires a balance between the structural performance and the thermal insulation of the grout material used to fill the annular space. In this study, the effect of aggregates $(4–19.1\mathrm{mm})$ , sand $(0.4–5\mathrm{mm})$ , and microspheres $(<0.2\mathrm{mm})$ on the bonding shear strength and thermal conductivity of a polyurethane-based polymer grout was investigated. The shear bonding strength between grout material and steel was determined using single-lap configuration. Addition of aggregate and sand improved the bonding strength. Hot wire method was used to determine the transient thermal conductivity $\left(k\right)$ of polymer-based insulator with and without filler materials. The average maximum bonding shear strength of polymer–aggregate and polymer–sand composite was $1.79\mathrm{MPa}$ $\left(260\mathrm{psi}\right)$ and $1.97\mathrm{MPa}$ $\left(285\mathrm{psi}\right)$ , respectively, with 60% of fillers (by weight) in the polymer composite. The average transient thermal conductivity of polymer was $0.091\mathrm{W}∕\mathrm{mK}$ , which was reduced due to the addition of microspheres and increased due to the addition of aggregates and sand. Based on published data a relationship between thermal conductivity and density was developed and verified with data from the current study. Also, relationships between thermal conductivity, pulse velocity, and bonding shear strength were developed using the test data.

Practical experience and laboratory observations indicate that corrosion affected reinforced concrete structures are prone more to cracking and delamination of the concrete than to the loss of structural strength. A review of research literature suggests that insufficient theoretical work on corrosion induced concrete delamination has been undertaken. This paper proposes a theoretical method to predict the time to concrete delamination caused by steel reinforcement corrosion. The method is based on fracture mechanics and uses crack opening in concrete as the criterion for its delamination. An analytical model is derived to determine the crack width in concrete. A numerical example is given to illustrate the proposed method and a comparison with both test results and an empirical model indicates a good agreement. It is found in the paper that the corrosion rate is the most significant single factor that affects the time to concrete delamination. The proposed method can be used for the prediction of time to concrete delamination for reinforced concrete structures located in chloride-laden environments. In principle, this provides a means for judging timely intervention and as such has the potential to prolong the service life of corrosion affected concrete structures.

Pond ash, after adequate stabilization, may be suitable for various engineering applications. The effects of lime stabilization on the strength and durability aspects of a class F pond ash, with a lime constituent as low as 1.12%, are reported. Lime contents of 10 and 14% were used, and the samples were cured at ambient temperature of around $30°\mathrm{C}$ for curing periods of 28, 45, 90, and $180\text{days}$ . Samples were subjected to unconfined compression tests as well as tests that are usually applied to rocks such as point load strength tests, rebound hammer tests, and slake durability tests. Unconfined compressive strength (UCS) values of 4.8 and $5.8\mathrm{MPa}$ and slake durability indices of 98 and 99% were achieved after $180\text{days}$ of curing for samples stabilized with 10 and 14% lime, respectively. Good correlations, that are particularly suitable for stabilized materials of low density and low strength, have been derived for strength parameters obtained from UCS tests, point load strength tests, and Schmidt rebound hammer tests, and also between UCS and slake durability index.

This paper presents an application of an optimization based on the Taguchi method for analyzing the deterioration of concrete with different compositions due to freezing and thawing. Effects of four parameters, i.e., water–cement ratio, cement content, amount of air-entrainment, and curing conditions, on the freeze–thaw resistance of concrete were investigated. The deterioration in concrete during the repeated freeze–thaw cycles were quantitatively evaluated in the light of the experimental measurements taken on length changes. It can be concluded that, within the limits of this work, the most important parameter affecting the freezing resistance of the concrete is the air-entraining admixture (AEA). Non-air-entrained concretes were severely damaged exhibiting substantial scaling after a limited number of freeze–thaw cycles. Damage increases significantly after around 1.5% residual length change (expansion) occurs in the specimens without AEA.