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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 111 Abstracts search results
September 1, 2021
M. C. de Moraes, I. S. Buth, C. Angulski da Luz, E. A. Langaro, and M. H. F. Medeiros
Recently, alkali-activated cement (AAC) has been studied to partially replace portland cement (PC) to reduce the environmental impact caused by civil construction and the cement industry. However, with regard to durability, few studies have addressed the behavior of AAC. This study aimed to evaluate the performance of AAC made from blast-furnace slag with contents of 4 and 5% sodium hydroxide as an activator (Na2Oeq of 3.72% and 4.42%, respectively) when subjected to alkali-aggregate reaction (AAR). Length variation tests were carried out on mortar bars immersed in NaOH solution (1 N of NaOH, T = 80°C [176°F]) and on concrete bars (T = 60°C [140°F], RH = 95%); compressive strengths tests and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses were also made. Two types of PC were used as a comparison. The results showed good behavior of the AAC in relation to the AAR, with expansions lower than those established by the norm (34% of the limit) and without the finding of losses of mechanical resistance or structural integrity. The alkaline activator content had a small influence on the behavior of the AACs, in which the lowest amount of NaOH (4%) showed fewer expansions (only 15% of the limit established by the norm). Even for the highest activator content (5%), the results were good and comparable to those of PC with pozzolans, which is recommended for the inhibition of AAR.
July 1, 2021
R. V. M. Toffolo, T. K. Moro, D. H. Santos, L. C. B. Costa, J. C. Mendes, and R. A. F. Peixoto
This work evaluates the technical feasibility of a roller-compacted concrete (RCC) pavement with complete replacement of natural aggregates by electric arc furnace slag (EAFS) or basic oxygen furnace slag (BOFS). The methodology includes, initially, the processing of the slags, and physical, chemical, and environmental characterization of the natural and slag aggregates. Subsequently, concrete mixtures were designed, and the compaction at optimum moisture was performed. Finally, the behavior of specimens under service and their mechanical performance were evaluated. Results show that both EAFS and BOFS enhance the RCC’s compressive strength and modulus of elasticity. The RCC produced with BOFS aggregates presented some expansibility due to its high contents of chemically active finer-than-75-µm materials and higher porosity. The EAFS aggregate was stable in durability analysis. In conclusion, through optimal mixture proportions and using compatible energy compression, it is viable to produce pavements with EAFS steelmaking slag in efficient, economical, and environmentally friendly manners. BOFS also showed promising results but requires further investigation.
November 1, 2020
Carbonation of concrete can cause the uptake of CO2 and alleviate the CO2 emissions burden of the concrete industry. This study shows a procedure for evaluating the CO2 uptake of fly ash (FA)-blended high-strength concrete, considering both the service and recycling stages. First, a blended cement hydration model is proposed to evaluate the contents of carbonizable substances, porosity, and CO2 diffusivity. In the service stage, a one-dimensional carbonation model is proposed for evaluating carbonation depth. In the recycling stage, an unreacted core model is proposed for evaluating the carbonation process of spherical crushed concrete. Second, CO2 uptake models are proposed for the service and recycling stages, considering concrete materials, structural elements, and environmental exposure. The total CO2 uptake ratio is determined as the sum of CO2 uptake in the service and recycling stages. The calculation results show that, as the FA replacement ratio increases from 0 to 40%, the CO2 uptake ratio in the service stage increases from 2.78 to 4.72%, and the total CO2 uptake ratio increases from 18.9 to 20.8%. As the surface to volume ratio of the structural element increases, or the size of particles of crushed concrete decreases, the rate of CO2 uptake increases but the total CO2 uptake ratio does not change.
September 1, 2020
Jun-Zhi Zhang, Xiao-Yun Zhou, Jing Zhao, Meng Wang, Yan-Hong Gao, and Yu-Rong Zhang
According to the main meteorological parameters and chloride concentration of field exposure tests, indoor artificial climate and dry-wet cycle simulated tests were designed to investigate the similarity of apparent and instantaneous diffusion coefficients in different ambient environments. Results show that chloride diffusion coefficients increased with water-cement ratio (w/c) and
decreased with exposure time, regardless of the environment. Besides, instantaneous diffusion coefficients are all less than the corresponding apparent diffusion coefficients; their differences decrease with the increasing of w/c and show first a decrease and then gradually an increasing trend with exposure time. Environmental factors have little effect on the similarity constant of instantaneous diffusion coefficients. A quadratic function can be used to describe the relationship between age reduction factors of apparent and instantaneous diffusion coefficients and w/c in different environments. According to the Second Similarity Theorem, specimens exposed to a natural tidal environment for 240 days can be simulated by that exposed to an artificial climate simulated environment for 80 days effectively.
July 1, 2020
Mahdi Valipour and Kamal H. Khayat
Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.
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