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.

LCPC (Central Laboratory for Roads and Bridges, a French public research laboratory) has developed for five years a new concept of concrete pavement. It is based upon the following ideas: - High-Performance Concrete shows unique qualities with regard to pavement applications, like high tensile strength, durability, freeze-thaw resistance, abrasion resistance and prevention of steel corrosion; - but economy does not promote the use of HPC in conventional pavement, since the gain in flexural strength leads to a decrease in slab thickness, which does not compensate the increase of material unit cost (i.e. the cost per unit surface increases when replacing normal- by high-strength concrete); - HPC qualities are mostly desirable at the top surface of the pavement. Therefore, HPC Carpet consists in a thin, 60-mm HPC wearing course, reinforced by a welded wire mesh, cast upon a conventional concrete (or cement-treated material) structural layer. Thanks to a complex of polymer and geotextile, there is no bond between the two layers, so that reflexive cracking from the base to the course layer is avoided. However, cracking due to traffic loads is permitted in both directions, the dense reinforcement being supposed to maintain the course layer integrity. The paper will give an overview of this research, which encompassed design calculations, thermal instability verification, fatigue tests on a 10-m full scale model and an experimental construction site near Lyon (France). Here, a 120-m long test section has been built in 2003, and is currently submitted to a heavy truck traffic. To date, the behavior is excellent. In conclusion, the economical potential of this new concept will be highlighted. Rehabilitation of old concrete pavements – where slabs are partly cracked, with moderate rocking – appears as a promising market.

This paper describes an approach used in developing a performance-based mixture design and optimization system for paving concrete. This system is being developed as part of a Federal Highway Administration (FHWA) project entitled “Computer-Based Guidelines for Job-Specific Optimization of Paving Concrete.” In this project, a new method of designing and optimizing concrete mixtures for pavement applications is being developed. The procedure includes two key elements: a knowledge base and mixture optimization routines. The former assists the user in selecting mixture design criteria based on site-specific conditions. It also allows for the user to quickly identify what combinations of concrete-making materials may be a starting-point for their site-specific conditions. The second element allows the user to optimize numerous properties of their concrete mixture including: w/cm ratio, cement content, the use of chemical and mineral admixtures, and gradation of aggregates. The optimization can be based on a variety of targets including cost, strength, workability, durability, and numerous other concrete mixture properties – both fundamental and phenomenological. Overall optimization of the selected targets is achieved using concepts of utility theory. When combined, these methods represent a rational approach to quantifying subjective decision-making criteria that is used in finding the optimum concrete mixture for specific conditions.

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.