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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 16 Abstracts search results
July 1, 2019
Wei Cheng, John R. Elliott, and Kenneth C. Hover
Crushed charcoal (biochar) was introduced into mortar as lightweight, high-carbon fine aggregate, at eight levels of sand replacement varying from 0 to 100% and up to 275% of cement content by mass. Carbon encapsulated in hardened mortar offset the carbon footprint of cement production and reduced demand for natural sand. Water content was increased to accommodate 125% biochar absorption and maintain workability. Mixture proportions affected water-cement ratio (w/c), fresh density, and compressive and splitting tensile strength of hardened mortar, with significantly diminished strength at increased biochar content. A net carbon benefit accrued when biochar content exceeded approximately 10% of the total aggregate mass or one-third of the cement mass. At this level, compressive strength is less than typically associated with structural concrete, but net sequestration of 800 kg carbon per m3 (1350 lb/yd3) could be realized at strength levels associated with controlled low-strength materials (CLSM). Multiple environmentally effective applications are suggested.
July 1, 2016
T. Raghavendra, M. Sunil, and B. C. Udayashankar
An increase in industrial and construction activities has resulted in the generation of wastes that consume large volumes of landfill spaces. Controlled low-strength materials (CLSMs) are an obvious choice for reuse of large quantities of these waste materials. This paper examines the fresh and hardened properties of CLSM mixtures produced using wastes such as bagasse ash and fly ash as pozzolanic materials, and broken hollow concrete blocks and quarry dust as fine aggregates. Engineering properties such as spread flow, Marsh flow, compressive strength, settlement, and density were investigated. Flow and strength phenomenological models were generated. The predicted values were also compared with Lagrange’s interpolation values and a new set of experimental
data. Results indicate that phenomenological models encourage the production of CLSM of required parameters instead of a conventional trial-and-error process. The use of fly ash, bagasse
ash, and quarry dust in large quantities increased water demand of the mixtures. Bagasse ash mixtures containing quarry dust resulted in lower strengths when compared to fly ash mixtures containing powdered hollow concrete blocks. All these wastes are encouraged to be reused in CLSM and, hence, reduce the burden on landfills.
March 1, 2015
Ricardo Serpell, Jacob Henschen, Jeffery Roesler, and David Lange
Controlled low-strength material (CLSM) mixture design remains a trial-and-error process. A new approach using relative proportioning of the constituent materials instead of prescribed mass contents is proposed. Relative proportions allow for independent adjustments that enable unbiased estimation of their effects on CLSM properties. For the CLSM mixtures studied, a central composite experimental design was defined using three relative proportions: volumetric paste percentage (VPP), water-cementitious material ratio (W/CM), and portland cement-total cementitious materials ratio (OPC/CM). Second-order response models for slump flow, subsidence, and 28-day compressive strength were obtained for different sets of constituents, including virgin and recycled concrete fine aggregates and two fly ash sources. Slump flow and subsidence were most affected by the VPP and W/CM, respectively, whereas strength was explained by the combined effect of the W/CM and OPC/CM. The W/OPC ratio was not a reliable predictor of CLSM strength.
Ceki Halmen and Harsh Shah
A series of low-cost controlled low-strength materials (CLSMs)mixtures were produced without cement, using only by-products, including Class C fly ash, large quantities of limestone quarry fines, and synthetic gypsum. Flow, setting time, compressive strength, elastic modulus, and freezing-and-thawing resistance of mixtures were evaluated. Results indicated that CLSM mixtures solely comprised of by-products can be designed to provide a wide range of flow, setting time, and strength values. Obtained flow values varied between 200 and 600 mm (8 and 24 in.), setting time varied between a couple of hours and a day, and strength values varied between 237.4 and 9932 kPa (34.4 and 1440.5 psi). The maximum measured mass loss after 12 freezing-and-thawing cycles was 8%. Results showed that the addition of synthetic gypsum significantly improved strength and freezing-and-thawing resistance of mixtures.
January 1, 2012
Lianxiang Du, Kevin J. Folliard, and Thanos Drimalas
Rapid-setting controlled low-strength material (RS-CLSM) is a special type of CLSM that is characterized by rapid setting, hardening, and early-strength development, making it well suited for rapid repair and accelerated construction. RS-CLSM mixtures are typically comprised of ASTM C618 Class C fly ash, sand, and water. In this study, research was performed to evaluate the effects of different Class C fly ashes and dosages, and the addition of various additives on the fresh properties and early strength of RS-CLSM mixtures. Two Class F fly ashes were used as additives at replacement levels of 5, 10, 15, 20, 25, 30, and 35% of Class C fly ash. The results showed that they were not effective in extending the flowability time window of RS-CLSM. Gypsum was added to RS-CLSM mixtures at dosages of 1, 2, 3, 4, and 5%. No significant retarding effects were found with the dosing levels. By contrast, the addition of hemihydrate was found to be more effective in changing the fresh properties when the same dosages as gypsum were used. Aluminum sulfate was found to be the most effective to delay or even prohibit the hydration of Class C fly ash for up to 24 hours, when dosages of less than 5% were used. The addition of Type I portland cement at levels of 1, 2, 3, and 4% was also studied and the effects differed with the Class C fly ashes used. Different possible reactions to explain the results are discussed. In summary, this study found that RS-CLSM mixtures made of different Class C fly ashes possess different fresh properties and respond differently to various additives; such knowledge may be applied to the optimization of RS-CLSM for desired workability, setting, hardening, and early-strength development.
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