United States Department of Transportation
i
Design and performance of crack-free environmentally friendly concrete "crack-free eco-crete".
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2014-08-01
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Abstract:High-performance concrete (HPC) is characterized by high content of cement and supplementary cementitious materials (SCMs).
Using high binder content, low water-to-cementitious material ratio (w/cm), and various chemical admixtures in the HPC can result in
higher material cost and greater risk of thermal and shrinkage cracking, thus reducing service life of the structure. This project seeks to
investigate the feasibility of producing crack-free and environmentally friendly concrete (crack-free and Eco-Crete) for building and
transportation infrastructure applications. Two types of concrete materials, including Eco-super workable concrete (Eco-SWC) and
Eco-self-consolidating concrete (Eco-SCC) are of special interest in this project. Eco-Crete mixtures are developed with a binder
content lower than 315 kg/m3 (530 lb/yd3). The concrete should develop 56-day compressive strength greater than 30 MPa (>4350
psi). Given the low binder content compared to the targeted performance level, binder composition and aggregate proportion are
optimized based on the packing density to reduce the voids between particles. The optimized concretes exhibit low shrinkage given
the low paste content and use of shrinkage mitigation approach, such as the use of a shrinkage reducing admixture (SRA), a Type G or
K expansive agent (EX), and a lightweight sand (LWS), as well as using fibers to reduce cracking. A factorial design approach was
also employed to quantify the effect of such materials on mechanical and shrinkage properties. The results indicate that, the combined
use of 10% silica fume with either 40% fly ash or 40% slag exhibited the highest packing density of 0.66 compared to 0.52 for cement
paste. The modified Andreasen packing model with distribution modulus (q) of about 0.29 fits reasonable well to express the particle
size distribution (PSD) of aggregate for SCC with low binder content. Binary shrinkage reducing materials containing 7.5% Type G
EX and 20% LWS or ternary system including 12.5% Type K EX, 2% SRA, and 20% LWS can be quite effective for developing Eco-Crete mixtures to exhibit crack-free properties.
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