Pierre-Claude Aitcin

High-performance Concrete

Foreword A. Neville. Introduction. Terminology. A Historical Perspective. The High Performance Concrete Rationale. High Strength Concrete Principles. Review of Relevant Properties of Some Ingredients of High Performance Concrete. Materials Selection. High Performance Mix Design Methods. Producing High Performance Concrete. Preparation for Concreting: What to do, How to do it and When to do it. Delivering, Placing and Controlling High Performance Concrete. Curing High Performance Concrete to Minimize Shrinkage. Properties of Fresh Concrete. Temperature Increase. Testing High Performance Concrete. Mechanical Properties. The Durablility of High Performance Concrete. Mechanical Properties. The Durability of High Performance Concrete. Special High-Performance Concretes. Ultra High-Strength Cement-Based Materials. A Look Ahead. Afterword P. Richard. Further and Recommended Reading

Mechanical Properties and Durability of Two Industrial Reactive Powder Concretes

Two reactive powder concretes (RPC) were produced on an industrial scale at the Universite de Sherbrooke and in a nearby precast plant. A 2.6 cubic meter mix was prepared in the central mixer of the precast plant. The ready mix RPC was sampled before and after the addition of steel fibers while the one produced at the precast plant was sampled only at the end of the mixing process. These RPCs were tested for compressive strength, modulus of elasticity, freezing and thawing cycling resistance, scaling resistance to deicing salts, and resistance to chloride ion penetration. The results show that a 200 MPa compressive strength could be achieved in both cases: after curing in hot water at 90 degrees C or in the low pressure steam chambers at the precast plant. Confinement of the RPC in a steel tube greatly increases its compressive strength and its ductility.

Optimization of high strength limestone filler cement mortars

Abstract The effect of limestone microfilier replacement of cement on the mechanical performance and cost effectiveness of low w c ratio superplasticized portland cement mortars was investigated. The experiments were designed based on a so-called uniform-precision factorial plan. Cement pastes of different w b ratios and incorporating various proportions of limestone powder and/or silica fume were designed to have a constant flow time. Mortars corresponding to the different cement pastes were made, their 1, 3, 7, 28 and 91 day compressive strengths were measured and their cost effectiveness was analyzed. The statistical approach used permitted the calculation of the isoresponse curves for the parameters under study over the experimental domain and the optimization of their effect.

Influence of Coarse Aggregate on Elastic Properties of High-Performance Concrete

The paper resports tests carried out on high-strength concrete made with differnt types of crushed rocks. These tests highlight the role played by coarse-aggregate through the elastic properties of the parent rock. The results obtained open an opportunity to review the present formulas relating E sub c to F sub c recommended by some codes.

ETTRINGITE FORMATION: A CRUCIAL STEP IN CEMENT SUPERPLASTICIZER COMPATIBILITY

Abstract The rheology of cementitious system containing superplasticizer is the consequence of a physical process due to the electrostatic repulsion between particles, but also of a chemical process linked to the nature of the phases that are formed. Ettringite crystallization play as a key role in this matter and the nature of the sulfate phase added to control cement setting is as important as its dosage. Alkali sulfates, which provide only SO 4 2− ions, do not promote the formation of ettringite for which the presence of large amounts of Ca 2+ is necessary. The adsorption of superplasticizer molecules on hydrated cement grains slows down the dissolution rates of the constituents and modifies the nature of the compounds formed. It could result in a modification of the ettringite morphology.

Self-consolidating concrete

As self-consolidating concretes (SCCs) are easily pumpable and require little workmanship to be poured, their use is gaining acceptance in casting columns, walls and floors for high-rise buildings. SCCs are also currently used in pre-cast plants because they facilitate and accelerate the pouring of concrete, prolong the life of the moulds and decrease the noise level in the plant. This noiseless aspect is a great advantage when casting concrete in buildings during working hours or in cities where there are noise restrictions after 5 pm. The formulation of SCC is flexible enough to accommodate the addition of fine materials or viscosity-modifying admixtures (VMAs) that are used to adjust SCC viscosity. The overall cost balance of using SCCs must be considered in a global sense. Using SCCs requires tighter quality control, but knowledge and practical experience are now available to handle this properly.

Binders for durable and sustainable concrete

Modern hydraulic binders can be used effectively with Portland cement and supplementary cementitious materials to produce durable concrete. They also provide a means of recycling by-products from other industries and of decreasing the emission of greenhouse gases. The first binders were discovered in ancient times when it was observed that new pozzolans mixed with lime could harden under water; and in the middle of the nineteen century the first artificial hydraulic binder, Portland cement, was discovered. By modifying the four basic oxides in the limestone and clay mix used in the production of Portland cement it is possible to modify significantly the practical properties of the clinker, and consequently the performance of the fresh and hardened concrete in which it is used. Chemical admixtures can be used to disperse cement particles without the use of extra water, and so make concrete which is highly resistant to penetration by aggressive agents and of high durability and strength. Supplementary cementitious materials or fillers can be mixed with Portland cement to produce modern hydraulic binders and improve the ecological performance of concrete. The hydration process of a modern hydraulic binder is becoming quite complex because it involves the chemical reactivity of Portland cement clinker, of supplementary cementitious materials and of different types of admixtures. This has already resulted in great technological achievements such as high-performance concrete, self leveling concrete, confined concrete, high-performance roller compacted concrete, fiber reinforced concrete, and reactive powder concrete.

DETERMINATION OF ELASTIC PROPERTIES OF HIGH - PERFORMANCE CONCRETE AT EARLY AGES

Knowledge of the elastic properties of concrete at early ages is very useful for designers, especially from a serviceability point of view. This paper discusses the determination at early ages of the elastic properties of three different concretes with water-cementitious materials ratios of 0.45, 0.35, and 0.30. Static and dynamic tests on the modulus of elasticity were carried out to monitor the evolution of this important parameter from 8 h of age and thereafter. A correlation factor between the static and dynamic moduli of concretes with a water/binder ratio between 0.30 and 0.45 is proposed. The relationship predicting the static modulus of elasticity of concrete was found to be proportional to the square root of the concrete compressive strength. The Poissons ratio was found to decrease sharply in very little time to reach a 0.14 value at a very young age, and then increased to approximately 0.24 after 7 days.

Sustainability of Concrete

Abstract The sustainability of concrete depends on both its material properties and its durability. The sustainability of concrete can best be improved by using a low w/b ratio, increasing the use of supplementary cementing materials and fillers, producing more durable concrete, designing more efficient concrete mixes by optimizing the particle packing, and better educating civil engineers about both cement and concrete production and the concept of sustainability. This chapter explores these and some related issues dealing with how to reduce the carbon footprint of concrete.

DEVELOPMENTS IN THE APPLICATION OF HIGH-PERFORMANCE CONCRETES

Abstract Over the last few years, the compressive strength of some of the concrete used has increased dramatically. In 1988, a 120 MPa concrete was delivered on site, while, until relatively recently, 40 MPa was considered indicative of high strength. The spectacular increase in compressive strength is directly related to a number of recent technological developments, in particular the discovery of the extraordinary dispersing action of superplasticizers with which flowing concretes can be made with about the same mixing water that is actually required to hydrate all the cement particles or even less. The reduction in water cement ratio results in a hydrated cement paste with a microstructure so dense and strong that coarse aggregate can become the concretes weakest constituent. Silica fume, a highly reactive pozzolan, considerably enhances the paste/aggregate interface and minimizes debonding when final failure occurs. Lastly, the use of supplementary cementitious materials, such as fly ash and especially slag, helps solve slump loss problems which become critical at low w c ratios.