International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

The effect of air entrainment on the compressive strength of high performance concrete is presented in this paper. Generally, an increase in the total air content of one percent decreases the compressive strength of concrete two to five percent. This rule of thumb was developed from research on normal strength concrete, but there is little data on the strength reduction due to entrained air in high performance concrete. The paper presents compressive strength test results of several high performance concrete mixtures with total air contents ranging from two to six percent. The compressive strength of the mixtures varied from 42.4 MPa (6150 psi) to 95.9 MPa (13,900 psi). The results of the study support the use of this rule of thumb for high performance concrete. Data are also presented on the increased dosage rate of air entraining agents required in low water to cementitious material ratio concrete.

As with other mineral admixtures, the use of rice-husk ash leads to an improvement of the concrete internal structure, reducing the pore size and particularly an improvement in the interface bond. In this sense it can be assumed that the failure mechanism can be modified, and the concrete will exhibit a more brittle behavior. That has a special interest in high-strength concrete and in the design of large concrete structures. This paper focuses on the fracture behavior of rice-husk ash concrete. A wide range of concrete strengths are analyzed including normal and high-strength mixtures. The flexural behavior was analyzed following the general guidelines of the RILEM 50-FMC using a center-point loading arrangement on notched beams of 400 mm span, measuring deflections and the crack mouth opening displacement (CMOD). In addition, the compressive strength and the elastic modulus were measured on standard cylinders. The effects of water-cementitious material ratio and the age of testing on the strength, energy of fracture and the characteristic length on concretes with and without rice-husk ash incorporation are discussed.

The prediction of concrete properties using computer modeling is becoming widely used, and many models utilize the concept of maturity. The original maturity concept was developed empirically from the study of the temperature effect on the compressive strength of normal-strength concrete. The use of the maturity concept for estimating the development of properties other than compressive strength has not yet been sufficiently validated with experimental data, especially for high-performance concrete. This paper presents a study of the maturity method for predicting the development of key properties of high-performance concrete, such as compressive strength, splitting tensile strength, modulus of elasticity, and level of cement hydration. The derivation of the maturity method is explained and experimental evidence, collected under different temperature conditions, is presented and discussed. The results were used to study the activation energy, which is a governing parameter of the Arrhenius maturity formulation, for predicting the key properties of high-performance concrete. Recognizing the need for a more accurate determination of the activation energy for each concrete property, a new practical approach for calculating the Arrhenius maturity index is proposed.

Mix design and technology of very high strength rapid-hardening concrete (VHSC) on the base of composite cements produced by «intergrinding» (IG) and «interblending» (IB) have been developed, and their characteristic properties have been studied. The use of mechanical-chemical activation of binders in combination with both new generation superplasticizers based on polycarboxilates and traditional ones and efficient dispersed fine mineral additives (silica fume, metakaoline, etc) allows to obtain VHSC. The strength ranged from 50-80 MPa after 24 hours and 125-140 MPa after 28 days of normal curing for self-leveling concrete mixtures (slump value 22-25 cm). Intensive concrete hardening starts after either 10 hours (IG) or 15 hours (IB) from mixing time. With the increase of hardening temperature ranging from 40 to 500C, the induction period decreases by 2-2,5 times, and strength of concrete exceeds 50 MPa in 8-10 hours after mixing (IG and IB, respectively). Volumetric water absorption of coarse aggregate concrete produced with water/binder ratio of 0.24-0.28 amounts to 2.2-3.3%, and that of fine-grained concrete, with water/binder ratio of 0.32-0.39, to 3-3.4%. Waterproofness of such concrete exceeds W20 (water tightness relating to Russian standard testing of cube specimen 150 mm in diameter and 50 mm in height under 2 MPa pressure during 6 hours), and their freezing-thawing resistance surpasses 600 cycles. Physical and mechanical properties (initial modulus of elasticity, tensile strength) are in line with the normal indices for corresponding concrete classes. Shrinking deformations of heavy weight concrete after 28 days of normal curing are 10x10-2 – 17x10-2 mm/m and those of fine-grained concrete are 29x 10-2 – 48x10-2 mm/m.