Marcel Cheyrezy

Composition of reactive powder concretes

Abstract Development of an ultra-high strength ductile concrete designated RPC (Reactive Powder Concrete), was made possible by the application of a certain number of basic principles relating to the composition, mixing and post-set heat curing of the concrete. RPC 200, which can be used under job site conditions similar to those for conventional high performance concretes, can be used in the construction of prestressed structures incorporating no passive reinforcement. RPC800 is suitable for precasting, and can achieve compressive strength values exceeding 600MPa. A value of 810MPa has been obtained with a mixture incorporating steel aggregate.

Microstructural analysis of RPC (Reactive Powder Concrete)

Reactive Powder Concretes (RPC) are characterized by high silica fume content and very low water to cement ratio. Granulometry and heat treatment were optimized to obtain excellent mechanical and durability properties. The study of several RPC compositions by Mercury Porosimetry, Thermogravimetric Analysis and X-ray diffraction made it possible to better understand their microstructural properties depending on their heat treatment. Influence of temperature on hydration and pozzolanic reaction were examined. For high temperature, the presence of a crystal hydrate, xonotlite, was observed. Mercury Porosimetry also showed that a minimum porosity could be obtained with selected heat treatment.

Investigation of hydration and pozzolanic reaction in Reactive Powder Concrete (RPC) using 29Si NMR

Hydration of RPC (Reactive Powder Concrete) and pozzolanic reaction were studied by 29Si NMR using SPE/MAS technique. Industrial cement and materials (silica fume, crushed quartz) constitutive of RPC imposed a careful study of spectra acquisition (relaxation times, spinning velocity).… Two RPC formulations were tested. Samples having undergone heat treatment at temperatures between 20 °C and 250 °C were investigated in order to gain a better understanding of the influence of temperature on hydration and pozzolanic activity. It was shown that silica fume consumption was highly dependent on heat treatment temperature and duration. Crushed quartz reactivity was also clearly demonstrated. It was proved to be dependent on heat treatment temperature and duration. Q3 peaks attributed to the presence of a crystal hydrate, xonotlite were identified at 250 °C. Microstructural changes in hydrates structure were also observed. Average CSH chain length was shown to increase with increasing heat treatment temperature.

29Si NMR study of hydration and pozzolanic reactions in reactive powder concrete (RPC)

Abstract A careful analysis of the 29 Si NMR signal of reactive powder concretes, composed of siliceous cement, silica fume, and crushed quartz, has been done in order to determine the hydration conditons on the kinetics of hydration.

Nuclear Relaxation of Water Confined in Reactive Powder Concrete

We use two complementary techniques to exhibit the microposity of the reactive powder concrete (RPC). The differential scanning calorimetry of water in RPC evidences pore sizes in the nanometer range. The proton NMR in RPC confirms this result. The typical frequency dependence of the measured proton relaxation rates proves unambiguously the influence of the paramagnetic impurities at the surface of the pores. A theoretical interpretation in terms of the biphasic fast exchange model and the proton nuclear paramagnetic relaxation of an hydrated ion at the surface of the pores allow to obtain an estimation of the average pore sizes. The measured fractional magnetizations confirm that RPC porosity mainly consists of pores with average sizes smaller than a threshold value.

Mechanical Properties of Four High-Performance Concretes in Compression at High Temperatures

ABSTRACT Experimental results of the high-temperature behaviour of 4 High-Performance Concretes are presented. The main properties needed for design are synthesised; this relates to the evolution of compressive strength and Youngs modulus versus temperature. The phenomenon of transient creep at high temperature is also presented. Experimental data and a master curve usable for design are developed.