Journal of Materials in Civil Engineering

This study investigated the fracturing of concrete under triaxial compression. The experimental program involved size effect tests of compression fractures of cylindrical specimens with small notches, large notches, and holes. The geometrically similar columns of large $\left(\lambda =32\right)$ , medium $\left(\lambda =16\right)$ , and small $\left(\lambda =8\right)$ slenderness using a size range of 1:2:4:8 (8 for only medium slenderness) were tested. The study’s columns were built of normal- and high-strength concrete, in which the maximum aggregate size was 10 mm. A strong size effect was observed in the results. It is shown that, with increasing strength, the size effect becomes more pronounced as the brittleness is increased.

The effect of replacing cement by pozzolanic materials was investigated. This was done by a systematic increase in pozzolanic material inclusion, and was evaluated using the Rapid Chloride Permeability Test. The materials used were fly ash, blast furnace slag (BFS), and silica fume. The blending was at the increasing levels of 25, 50, and 70% of fly ash or BFS, with or without addition of silica fume at 10% cement replacement to form binary and ternary blends. A commonly practiced initial curing regime of seven days was administered. The experimental results obtained in this study were analyzed using statistical methodology. The results indicated that an increase in fly ash content increased the charge passed in the specimens but the reverse trend was observed with increase in the BFS content in the absence of silica fume. Silica fume alone as well as its ternary blend with 25% fly ash showed lower charge when compared with the control or with the binary blend of cement and fly ash. However, in ternary blends containing fly ash at more than 25%, the presence of silica fume did not cause a reduction in the charge. All ternary blends comprising BFS and silica fume passed lower charges than the respective binary blends. These ternary blends exhibited dense microstructure compared to the corresponding binary fly ash blends. The highest percentage replacement of cement with 70% BFS and silica fume was comparable with the addition of silica fume alone. The results showed that concretes with BFS blends exhibit lower charge passed and higher compressive strength than comparative blends using fly ash.

Two commercially available chemical dust palliatives were evaluated in full-scale experiments in an enclosed, controlled environment to evaluate their effectiveness and to determine impacts to a stabilized surface. The dust palliatives were topically applied at multiple application rates to the surface of a silty sand soil that had been stabilized using a combination of Portland cement and polypropylene monofilament fibers. Simulated traffic was applied to enclosed test sections using the heavy vehicle simulator-aircraft fitted with a C-17 aircraft tire at 15,560 kg (34,300 lb) load. The effectiveness of the dust palliatives was quantitatively measured using both gravimetric and optical detection devices. Results from the experiment show nearly complete reduction in dust for Palliative 2 (a synthetic oil) and heavy applications of Palliative 1 (an emulsion polymer). The methodology used for experimentally determining the dust palliative effectiveness provided a mechanism for reducing environmental influences that often invalidate and confuse the results of field experimentation data.

Wood-plastic composites have been recognized as versatile and practical materials for use in many light-structural uses. Recently, more structurally demanding applications have surfaced, which require an improved understanding of mechanical performance and design methodologies. Research addressing the influence of service temperature on mechanical performance with the goal of assigning structural design values is lacking. This study examines the effect of temperature on the mechanical performance of a polypropylene-pine composite formulation. Static tests were performed at temperatures between 21.1 and $80.0°\text{C}$ to determine the material constitutive relations and ultimate properties in tension and compression. A statistical approach was proposed to assess design thermal loads according to geographical location. Both Young’s modulus and ultimate stress were found to decrease with temperature while maximum strain increased linearly with temperature. Temperature adjustment factors were developed over the range studied and were found to decrease properties by as much as 50% at the highest service temperatures. A simple thermal load methodology based on an ASHRAE standard was proposed for determining prevailing thermal conditions in design.

The interpretation of half-cell potential measurements in reinforced concrete structures can be a major challenge for civil engineers. The main reason for this is that half-cell potential mapping provides information to predict the probability of corrosion in concrete, but it does not give clear insight on the rate and the nature of corrosion. Although for general uniform corrosion, half-cell data can provide valuable information about the probability of corrosion. In the case of localized corrosion, the predictions of half-cell measurements can be misleading. The main objective of the present work is to provide practicing engineers a tool that they can use to better interpret the results of half-cell potential measurements. This tool quantitatively relates the potential readings on the surface of the concrete to the rate of probable localized reinforcement corrosion through concrete resistivity, cover thickness, and temperature, allowing the engineers to gain supplementary information from half-cell tests. Experimental comparisons presented in this paper demonstrate the potential benefits of the proposed approach when typical half-cell measurements may not be able to predict the localized corrosion mechanism.

Various methods of nondestructive testing offer the opportunity to understand hydration of cement-based materials. In particular, the ultrasonic wave reflection method does not require access to two sides of a structural member and can be performed continuously and on site. This advantage is very significant when estimating the in situ compressive strength of early-age concrete. However, it is also necessary to understand which properties are measured by the ultrasonic wave reflection method and compare the measurements with other testing methods. This paper demonstrates the nature of these measurements with the wave reflection method by comparing the results of the other nondestructive testing method using resonant frequencies.

Microwave transmission (and reflection) properties measured from diverse sides of prepared hardened mortar specimens with different water-to-cement ratios ( $w/c=0.4$ and 0.7) and sand-to-cement ratios ( $s/c=1.5$ and 2.0) are shown. Measurements were carried out by a simple and inexpensive free-space setup at three discrete frequencies ( $f=8.5$ , 10, and 12 GHz) in $X$ -band (8–12 GHz) during 3–36 months after specimens’ preparation. A recently developed approach (relative difference approach) is applied to predict the state and degree of aging (curing) of specimens using transmission properties obtained from various sides of specimens. It is observed that while reflection properties of specimens are nearly constant, their transmission properties and aging changed, except for the last few months, during 3–36 months. After approximately 30 months, aging of all specimens became constant. It is shown that, for measurements acquired from the same side of specimens with any $s/c$ ratio, the mortar specimen with a higher $w/c$ ratio $\left(w/c=0.7\right)$ will lose free water faster than the other specimen $\left(w/c=0.4\right)$ over approximately 3–9 months (first stage) of curing. In this stage, the effects of $s/c$ ratio and the operating frequency on temporal differences in transmission properties are not considerable. On the other hand, the mortar specimen with a lower $w/c$ ratio $\left(w/c=0.4\right)$ will drop free water sooner than the other specimen $\left(w/c=0.7\right)$ during approximately 9–30 months (second stage) of curing. In this stage, while the effect of $s/c$ ratio on temporal differences in transmission properties is still negligible, that of the operating frequency is highly pronounced.

Concretes with binary and ternary blends of portland cement, finely ground fly ash and finely ground granulated blast furnace slag were produced to investigate their effects on compressive strength and rapid chloride permeability. Portland cement was partially replaced by finely ground fly ash (Blaine specific surface: $604{\text{m}}^2/\text{kg}$ ) and finely ground granulated blast furnace slag (Blaine specific surface: $600{\text{m}}^2/\text{kg}$ ). Two series of concrete with water/binder ratios of 0.60 and 0.38 were produced and for both water/binder ratios, portland cement was replaced by: (i) 50% fly ash; (ii) 50% blast furnace slag; and (iii) 25% fly $\text{ash}+25\%$ blast furnace slag. At the high water/binder ratio, compressive strengths of the concretes with the pozzolans are lower compared to that of the portland cement concrete. At the low water/binder ratio, however, these strength reductions are less compared to the high water/binder ratio and compressive strength of the concrete produced with 50% slag was even higher than the portland cement concrete. The test results indicate the ground fly ash and ground granulated blast furnace slag greatly reduce the rapid chloride permeability of concrete. It was concluded that to reduce the chloride permeability of concrete, inclusion of pozzolans are more effective than decreasing the water/cement ratio.

Masonry is the oldest building material that survived until today, being used all over the world, and is present in the most impressive historical structures. There is a considerable amount of existing masonry buildings using granite as a masonry unit. Conservation, rehabilitation, and strengthening of the built heritage and protection of human lives are clear demands of modern societies and the evaluation of the stability conditions of damaged ancient constructions involves frequently the usage of more advanced numerical tools than linear elastic analysis, where the knowledge of the mechanical properties of the stone masonry is required. This work aims at obtaining the compressive mechanical properties and at improving the understanding of the fracture process of granites. Based on an enlarged experimental program of uniaxial compressive tests in different granite lithotypes, it was possible to obtain complete stress-strain diagrams through an appropriate circumferential displacement control, from which the elastic and fracture properties were derived. A comprehensive discussion on the parameters influencing the compressive behavior of granite such as planar anisotropy, weathering state, and physical properties are also provided.

The influence of water-to-cement mass ratio $\left(w/c\right)$ 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, semiadiabatic temperature, setting time, autogenous deformation, and strength development. Measurements of these properties using a single cement are presented for four different $w/c$ , ranging from 0.325–0.425. Some of the measured properties are observed to vary widely within this range of $w/c$ ratios. The heat release and setting time behaviors of cement pastes are contrasted. While early-age heat release is relatively independent of $w/c$ , the measured setting times vary by several hours between the four $w/c$ investigated in this study, indicating the fundamental differences between a physical process such as setting and heat release, which is purely a quantification of chemical reaction. While decreasing $w/c$ certainly increases compressive strength at equivalent ages, it also significantly increases autogenous shrinkage and may increase semiadiabatic temperature rise, both of which can increase the propensity for early-age cracking in cement-based materials.

Spalls and wide cracks represent functional and structural distresses in portland cement concrete pavement. Traditionally, these distresses were repaired by partial depth repair (PDR). The performance of PDR varies substantially. Two types of polymeric patch materials, Material-A and Material-B, were used to repair spalls and cracks. Material-A was used to repair spalls in continuously reinforced concrete pavement. It provided quite satisfactory performance for more than $6\text{years}$ . Material-B was used to repair cracks in jointed concrete pavement. Its performance was satisfactory when applied to stable slabs. Compared with full-depth repair (FDR), PDRs utilizing polymeric patch materials is much more cost effective, and PDR takes much less time than FDR. It was found that chip-and-patch method would work as well as saw-and-patch method as long as the repair limits include all the delaminated areas.

The length change and strength of mortar containing metakaolin (MK) and fly ash (FA) were investigated. Cement was partially replaced with 0–10% MK and 0–60% FA. Mortar specimens were subjected to water and mist curing at $20°\text{C}$ and air curing at $20°\text{C}$ and 60% relative humidity. The results show that there is noticeable shrinkage in mortars subjected to air curing, especially during the first 28 days. Beyond that age, there is little change in length. Increasing FA content under air curing reduced shrinkage. The incorporation of both 5% and 10% MK with varying amounts of FA further reduced shrinkage especially at 10% MK. As what can be expected, all mortars subjected to water curing exhibited an increase in length. Expansion was reduced when FA was present in the mix. However, mortars containing MK exhibited an increase in expansion under water curing with and without the inclusion of FA. Generally, for specimens subjected to mist curing, an expansion occurs during the first 15–30 days and beyond this age, shrinkage begins to take place. Replacing cement with 5% or 10% MK increases the compressive strength of mortar. The pozzolanic reaction of FA seems to get reduced as a result of preferential MK activity.