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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 22 Abstracts search results
January 1, 2019
Qi Cao, Quanqing Gao, Jinqing Jia, and Rongxiong Gao
To improve the early-age cracking resistance of self-consolidating concrete (SCC), this paper investigated the effects of an expansive agent (EA), fibers, and the interaction between EA and fibers on the cracking behavior of restrained SCC caused by plastic shrinkage based on the slab test. Twenty-one types of samples were prepared, including one control group, two EA contents (6 and 8% of the mass fractions of cementitious materials), three steel fiber contents (0.25, 0.50, and 0.75% by volume), three polypropylene fiber contents (0.05, 0.10, and 0.15% by volume), three hybrid fiber contents, and nine combinations of EA (8% of the mass fraction of cementitious materials) and fibers. The initial cracking time and propagation of cracks over time were both observed. Test results indicate that an increase of EA dosage presents no significant improvement on early-age cracking resistance capability. Compared with steel fiber (SF), polypropylene fiber (PP) with equivalent fiber factors was particularly effective in reducing the nominal total crack area. In general, crack reduction factors of fiber-reinforced expansive self-consolidating concrete (FRESCC) are 70% greater than that of SCC containing fiber only. It indicates that the combination of EA and fibers enable SCC to present better early-age cracking resistance.
Edward (Ted) G. Moffatt and Michael D. A. Thomas
Ettringite-based binders are used in niche applications that require a high compressive strength in a very short period of time to minimize construction times and disruption to the traveling public or user. High early strength is achieved due to the formation of ettringite within the first few hours of hydration, which results in a non-expansive system capable of reaching strengths of approximately 20 MPa (2900 psi) in the first 3 hours of hydration. Ettringite-based binders also carbonate at a faster rate than ordinary portland cement (PC)-based systems as a result of the limited amount or absence of portlandite (CH). Carbonation results in the conversion of ettringite into products that occupy less space, resulting in a loss of strength and increased porosity. The formation of ettringite is achieved through the use of systems composed of calcium aluminate cement (CAC, main phase CA) and calcium sulfate (CS), or calcium sulfoaluminate cement (CSA, main phase C4A3S) interground with calcium sulfate. In many cases, ettringite-based binders are used to accelerate ordinary PC-based systems to achieve a relatively high compressive strength and a suitable working time while still maintaining the hydration characteristics of PC. This study compared the performance of carbonated and noncarbonated concrete in terms of the resistance of the near-surface concrete to deicer-salt scaling and chloride ion penetration. Chloride binding tests were also conducted on the carbonated and noncarbonated cement paste samples and mechanical properties conducted on mortar specimens. The results show that CSA-based binders carbonate at a much faster rate than both CAC and PC based systems as a result of the increased ettringite content within the system. A decrease in the mechanical properties of carbonated ettringite-based binders is also observed as a result of the conversion of ettringite.
November 1, 2018
Matthew O’Reilly, Omid Farshadfar, David Darwin, JoAnn Browning, and Carl E. Locke Jr.
Corrosion-related cracking in reinforced concrete is caused by expansive corrosion products and the resulting tensile stresses. While the amount of corrosion to cause cracking has been studied for uncoated conventional reinforcement, significantly less is known about the corrosion loss at cracking for galvanized reinforcement. Conventional and galvanized bars were cast in chloride-contaminated concrete. Clear cover to the bar ranged from 0.5 to 2 in. (12.7 to 51 mm). Specimens were tested both with and without the use of impressed current to drive corrosion. It was found that galvanized reinforcement requires greater corrosion losses to crack concrete than conventional steel reinforcement. Visual observations at autopsy suggest that the cracking of the concrete specimens containing galvanized reinforcement was not due to zinc corrosion products, but rather to corrosion products from intermetallic iron-zinc layers or from the underlying steel. Further study is needed to determine the exact nature of these corrosion products. Tests using impressed current may be used to establish the corrosion loss required to cause cracking.
July 1, 2017
Ardavan Ardeshirilajimi, Di Wu, Piyush Chaunsali, and Paramita Mondal
Calcium sulfoaluminate (CSA) cements were developed for shrinkage compensation of concrete. The expansive nature of CSA-based cements can be used to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. Because of the higher water demand of CSA cement for achieving full hydration, as compared with ordinary portland cement (OPC), elevated water-cement ratios (w/c) for OPC-CSA cement blends are required for a successful mitigation of shrinkage. This study examines the effects of presoaked lightweight aggregate (LWA) addition on deformation properties of OPC-CSA mortar and concrete as an alternative to increasing the w/c. The motivation behind this work is to promote CSA hydration and increase the early-age expansion of OPC-CSA blends by curing concrete internally while avoiding the undesirable impacts of increased w/c on the microstructure of the mixture. The influence of LWA addition on autogenous and drying shrinkage of OPC-CSA blend was studied. It is shown that the early-age expansion of OPC-CSA blends can be dramatically increased when internal curing is implemented using LWA. Based on thermogravimetric (TG) results, it is indicated that the increase in expansion is partially due to the enhanced hydration of CSA cement in the mixture, which results in an increased rate of ettringite formation. Furthermore, the effects of LWA on total capillary porosity and compressive strength of OPC-CSA blends was also examined to verify the benefits of using LWA to promote CSA hydration as compared to increased w/c.
November 1, 2015
Mohammad R. Irshidat, Mohammed H. Al-Saleh, and Sura Sanad
The impact of partial substitution of cement particles with nanoclay on the expansive potential of cement mortar due to alkali-silica reaction (ASR) was investigated. Portland cement was replaced by 0.5%, 1%, and 2% montmorillonite nanoclay. The effect of ASR on compressive strength, chemical composition, and microstructure of nanoclay-cement composites was evaluated. The accelerated mortar-bar method was followed to perform the ASR test according to ASTM C1567. The experimental results showed that the expansion of cement mortar due to ASR can be reduced by the addition of nanoclay. Two percent nanoclay was the only dosage among others used in this study that can mitigate the expansion. Furthermore, the ASR caused a marginal enhancement in compressive strength of mortar compared to the specimens cured in water. The gain in strength reached up to 10% for mortars contacting 2% nanoclay. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis did not detect the formation of any secondary products due to the ASR, revealing the similarity between ASR and the pozzolanic reaction for the first 14 days of the reaction. However, the microstructure of the mortars became denser and more homogeneous when a part of cement was replaced by nanoclay.
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