In recent years, ultrarapid-hardening cement concrete has been widely used for the repairing works of concrete structures. The purpose of this study is to establish the mix design method for the ultrarapid-hardening cement concrete. The ultrarapid-hardening cement concrete was prepared with various unit cement contents, water-cement ratios, sand-aggregate ratios and retarder-cement ratios at 10, 20 and 30°C, and tested for slump, air content, handling time (which was defined as the elapsed time when the slump decreased to about 2cm) and compressive strength.
The conclusions obtained from the test results are summarized as follows:
(1) The slump of the ultrarapid-hardening cement concrete with various mix proportions may generally be expressed by the following equation at 10, 20 and 30°C:
Sl=
Ae-B(Va+Vc)/Vw where
Sl is the slump of the ultrarapid-hardening cement concrete,
Va, Vc and
Vw, are the volumes of aggregate, cement and water per unit volume of the ultrarapid-hardening cement concrete respectively, and
A and
B are empirical constants.
(2) The compressive strength and handling time of the ultrarapid-hardening cement concrete with various mix proportions may generally be expressed as a function of “water-cement ratio (α)” and “retarder-cement ratio (β)” by the following equations at 10, 20 and 30°C:
F=
A/(
Bα·
Cβ)
Ht=
A·
Bα·
Cβwhere
F and
Ht are the handling time and compressive strength of the ultrarapid-hardening cement concrete respectively, α is the water-cement ratio (α=
Vw/
Vc), β is the retarder-cement ratio (β=
Vr/
Vc), and
A,
B and
C are empirical constants.
(3) A mix design system for the ultrarapid-hardening cement concrete is proposed by use of the respective equations for slump, handling time and compressive strength predictions.
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