Abstract
The article deals with the selection of a suitable hardening accelerator for cement composite material for mass production of masonry blocks. The blocks contain cement and finely ground recycled concrete in ratio 1:1. Three different hardening accelerators in different quantity were tested for possibility of fast removing formwork. The dynamic modulus of elasticity was measured by non-destructive resonance method to determine the initial strengths. The modulus of elasticity was measured 7 and 12 hours after sample production to determine the increase in initial strength. Subsequently, the modulus of elasticity was measured at 1, 7, 14, 21 and 28 days after production of the test specimens. The resulting moduli of elasticity were compared with reference samples.
Highlights
Old waste concrete from damaged or destroyed structures has the risky properties because of different attributes and inhomogeneity of this waste, which are caused by the presence of other materials from building demolitions
The dynamic modulus of elasticity value of each set was calculated by the arithmetic mean of all 3 samples in the set
From the growth of the dynamic modulus of elasticity Edyn follows that the maximum increase in Edyn is within the first 7 days
Summary
Old waste concrete from damaged or destroyed structures has the risky properties because of different attributes and inhomogeneity of this waste, which are caused by the presence of other materials from building demolitions (bricks, wood, glass, reinforcement, etc.). Waste concrete sorting is negatively reflected in the price of this raw material. Recycled concrete is most often used as a base layer under the roadway. A recycle fraction greater than 1 mm is used, the use of finer fractions brings many complications and additional financial costs [1, 2]. The paper deals with the measurement of the dynamic modulus of elasticity of samples from the early hardening phase up to the age of 28 days. The samples contain cement and recycled concrete in weight ratio 1:1, mixing water and various hardening accelerators
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