Journal of Materials in Civil Engineering

The first rarely mentioned fundamental assumptions for the strength versus water-cement ratio relationship are discussed, namely, that: (a) the strength of structural concrete is controlled by the strength of the cement paste in it; (b) the strength of a cement paste depends strongly on the porosity in it; and (c) the porosity (capillary) is a function of the water-cement ratio. This is the foundation of the relationship between concrete strength and water-cement ratio. Numerous empirical formulas, so-called strength formulas, have been developed for this relationship; the Abrams’ formula for instance. These formulas estimate the concrete strength from the water-cement ratio only, and they are usually simple but have restricted limits of validity. For improvement, a new type of strength formulas is offered in this paper, formulas that have a second independent variable beside the water-cement ratio, such as the cement content, or water content, or paste content, etc. Such augmentation (a) improves the accuracy of the strength estimation; (b) shows that if two comparable concretes have the same water-cement ratio, the concrete having the higher cement content has the lower strength; and (c) shows that the magnitude of the changes in concrete strength depends on how the water-cement ratio is changed, by changing the cement content or the water content. Experimental data support these expectations. A formula is also presented for the effect of the other kind of porosity, the air content on the concrete strength. The combination of this with any good strength formula gives good fit with experimental results both of air-entrained and nonair-entrained concretes.

In this paper, phosphate and fluoride were added into the gypsum, respectively, to simulate phosphate and fluoride in the phosphogypsum. The affect of adding different impurities on setting time, compressive strength, and bulk density were inspected by simulation experiments. The pore structure of hardened gypsum was analyzed by mercury intrusion porosimetry, and the micromorphology of hardened gypsum was observed by scanning electric micrograph in sequence to get the influencing rule of different impurities and its contents on the performance and micromorphology of phosphogypsum. The results indicate that phosphate prolongs the setting time, while the fluoride shortens it. Meanwhile, the strength gets lower because of the coarsening crystal resulting from the phosphate and fluoride.

Joint sealants are used widely in Canada to protect pavements from infiltration of water and incompressible materials. Sealants are typically selected based on field studies, which are commonly repeated on a 10-year cycle. This paper examines a laboratory evaluation method based on two laboratory tests that are commonly used for testing asphalt binders: dynamic shear rheometer (DSR) and bending beam rheometer (BBR). Creep stiffness, rate of change in creep stiffness, and rate of change in complex shear modulus with temperature were used to evaluate sealant performance in cold climates. A sealant ranking system was proposed based on the calculation of a sealant index, which combines the proposed evaluation criteria. This method can potentially provide a cost-effective and rapid alternative to field studies. Eight hot-pour sealants were evaluated using this method. Results were verified from an ongoing field study that started in 2004. A good correlation was found between the proposed simplified evaluation method and the existing method.

In this study, the effects of the use of corncob, wheat straw, and plane leaf ashes (CA, WSA, and PLA) as mineral admixtures on concrete durability were investigated. Ten concrete mixtures were produced in three series with control mixes having $400\mathrm{kg}$ cement content. The control mixes were modified with 2, 4, and 6% of CA, WSA, and PLA in place of fine aggregate. To establish the durability of concrete, the compressive strengths were measured after 7, 28, 90, 180 days, and 18 months under sodium sulfate solution. In the meantime, abrasion resistance and water penetration were investigated. Test results indicate that CA, WSA, and PLA addition provides good workability and abrasion resistance compared to conventional concrete. Test results also showed that minimum abrasion resistance is obtained from the control specimen, while maximum abrasion resistance is obtained from CA3 (6%) specimens. Abrasion resistance is increased as the rate of fine CA, WSA, and PLA is increased. The results indicate that the increase in ash content caused a significant increase in the sodium sulfate resistance of the concretes. Hence, concrete with CA, WSA, and PLA addition can be recommended for the production of durable concrete.

The durability of concrete structures is strongly affected by the ease of water and ion penetration. Polymeric surface treatment with epoxy and silane are commonly used to provide a barrier to the ingress of water and ions. In this investigation, the improvement of barrier properties of epoxy and silane by the incorporation of nanosized organoclay was studied. The water vapor transmission test and the salt spray resistance test were conducted to evaluate the resistance to moisture and chloride penetration, respectively. The test results indicate significant improvement in moisture penetration resistance when small amounts of organoclay, ranging from 1 to $5\mathrm{wt}\%$ , are introduced into neat epoxy and neat silane. Polymer/organoclay nanocomposites are also more effective than neat polymers in inhibiting the ingress of chloride ion into the concrete, with $3\mathrm{wt}\%$ epoxy/organoclay nanocomposites showing the best performance. The results demonstrate the potential application of polymer/organoclay nanocomposites as a surface treatment material for concrete structures.

Effective structural use of steel fiber-reinforced concrete (SFRC) relies on the assumption of uniform dispersion of fibers within the elements. Fiber dispersion related issues hence stand as a cutting edge research and technology development topic. The use of self-consolidating concrete (SCC), thanks to its rheological stability and self-placability, which leads to the elimination of compaction by vibration, may be helpful in guaranteeing a uniform dispersion of fibers. With reference to the latter, several techniques [e.g., based on alternate current impedance spectroscopy (AC-IS), microwave reflectometry etc.] have been developed in the last few years for its nondestructive monitoring. Investigation into the connections between fiber dispersion and the performance of the composite in the fresh and hardened state stand as the natural completion for a thorough assessment of the FRC properties, aimed at promoting its wider use for full load bearing structural applications. This paper presents the results of a research project aimed at the above said purpose. Based on a previously calibrated mix-design methodology, suitable specimens were cast with SFRC characterized by different performance in the fresh state (vibration-, self-, and segregation consolidating) and tested in four-point bending, in order to assess the connections among fresh state behavior and fiber dispersion, herein investigated by means of AC-IS, and the performance in the hardened state. The results, highlighting this correlation, point out their importance for a design of the material composition “tailored” to the anticipated mechanical performance and to the specific structural application.

The influence of cement fineness on early-age properties of cement-based materials is investigated using a variety of experimental techniques. Properties that are critical to the early-age performance of these materials are tested, including heat release, temperature rise, chemical shrinkage, and autogenous deformation. Measurements of these properties for two cements of widely different fineness are supplemented with other performance measures, specifically acoustic emission measurements to listen for microcracking occurring in high performance $w∕c=0.35$ mortars and dual-ring paste shrinkage measurements conducted under sealed conditions to assess residual stress development. The measured properties are observed to be quite different for the coarse and the fine cement. The current emphasis on high early-age strength within the construction industry may result in the specification of cements that are more prone to early-age cracking.