The Young's modulus of concrete should be at least 0.8 times of the value calculated by the equation in JASS 5 (AIJ calculated value). Whereas one of the major factors affecting the Young's modulus of concrete is the Young's modulus of coarse aggregate, the information on the Young's modulus of coarse aggregate that satisfies the target value of JASS 5 is not shown clearly. Furthermore, whereas it is necessary to confirm the Young's modulus of concrete of the mixture proportion which is more dangerous than the actual mixture proportion prior to the construction, the definition of "more dangerous mixture proportion" is not shown clearly. In this study, based on the results of experiments for high strength concretes using crushed stones with the maximum size 20 mm, the influences of the Young's modulus and volume of coarse aggregate on the Young's modulus of concrete were investigated.
An ordinary portland cement and a cement for high strength concrete containing silica fume were used as cements. Mainly, an andesite crushed sand was used as fine aggregate. Three kinds (andesite, hard sandstone, limestone) of crushed stones were used as coarse aggregates. Using specimens (φ50×100 mm) taken from ores, the compressive strength and the Young's modulus of coarse aggregates were measured. Range of water-cement ratio of concrete was 0.15-0.40. Range of absolute volume of coarse aggregate per unit volume of concrete was 0.09-0.36 m3/m3. Additionally, the mortars of mixture proportions which are removed coarse aggregates from concretes were produced. Preparing standard cured specimens (φ100×200 mm) of concretes and mortars, the compressive strength and the Young's modulus of them were measured at the ages of 7, 28 and 91 days.
It was confirmed that the Young's modulus of high strength concrete is possible to be estimated based on the Young's modulus and the component ratio of each phase (mortar and coarse aggregate). However, in the case which the Young's modulus of concrete was small, the measured value tended to be slightly smaller than the estimated value by Hashin-Hansen equation3). Thus, by combining the equations for estimating the Young's modulus of mortar and concrete and for estimating the compressive strength of concrete6),9), the evaluation method of the relationship between the compressive strength and the Young's modulus of concrete based on the Young's modulus of coarse aggregate was proposed. The Young's modulus of coarse aggregate was evaluated to be between 5.5-7.0×104 MPa by this proposed method when the Young's modulus of concrete was about the same value as AIJ calculated value. On the other hand, the Young's modulus of coarse aggregate was evaluated to be about 4.0×104 MPa by this proposed method when the Young's modulus of concrete was about 0.8 times of AIJ calculated value. Based on this results, the reference value of the Young's modulus lower limit of coarse aggregate was shown as 4.0×104 MPa in order to meet the target value of the Young's modulus of concrete in JASS 5.
