Brittle Matrix Composites 9

The subjects of the symposia are on composite materials behaving as brittle, normal and special conditions of exploitation. Brittle matrix composites are applied in various domains and the series of symposia are closely related to their applications in civil engineering. In the last decades their importance is increasing along with their variety and the use of most advanced methods of testing. Papers include concretes, fibre concretes and ceramics, particularly their composition, microstructure and fracture processes. Various new and advanced engineering problems are presented in the papers.

The subjects of the symposia are on composite materials with matrices behaving as brittle in normal or special conditions. Brittle matrix composites are applied in various domains (civil engineering, mechanical equipment and machinery, vehicles, etc.) and in the last decades their importance is increasing together with their variety. Papers include: aggregate-binder composites (concretes, fibre concretes, rocks); sintered materials (ceramics); high strength composites with brittle matrices. In principle, the general problems of structures made of composite materials are not included in the papers. Various approaches to the material engineering problems are presented in the papers.

The subjects of the symposia are on composite materials with matrices behaving as brittle in normal or special conditions. Brittle matrix composites are applied in various domains (civil engineering, mechanical equipment and machinery, vehicles, etc.) and in the last decades their importance is increasing together with their variety. Papers include: aggregate-binder composites (concretes, fibre concretes, rocks); sintered materials (ceramics); high strength composites with brittle matrices. In principle, the general problems of structures made of composite materials are not included in the papers. Various approaches to the material engineering problems are presented in the papers.

The International Symposium in Brittle Matrix Composites October 13-15, 2003 covers a wide spectrum of topics including cement based composites, ceramic composites and brittle polymer matrix composites. In the papers various topics and issues are considered such as: analytical and numerical studies related to the design of composites, prediction of behaviour and verification of strength and stability, testing methods, manufacturing processes and repair, environmental effects and durability assessment. The present volume of 55 papers proves that there are still many problems in the field of brittle matrix composites deserving theoretical and experimental investigations and that new solutions to these problems are needed for practical application in civil engineering, industrial structures, machinery and other domains.

This paper presents the results from an experimental study on the behaviour of Reactive Powder Concretes (RPC) at high temperature. The exposure to high temperature is related to the potential risk of fire. A previous study has shown that RPC is prone to spalling in such circumstances and for this reason polypropylene fibres were used in RPC concrete to prevent this occurring. The addition of PP fibres reduces the risk of spalling due to an increase in permeability, however it reduces the initial compressive strength of the RPC material by approx. 20 %. The results demonstrate that the strength of concrete along with the modulus of elasticity decrease with increasing temperature. Two experimental concretes were prepared and prismatic specimens, 40x40x80mm in size, were cast from each mixture and tested in compression after being submitted to the high temperature. The relative value of compressive strength course for both types of concrete shows a similar development. The change in modulus of elasticity with temperature was determined from the stress-strain relationship and compared with the dynamic modulus of elasticity determined with the use of a Pundit plus ultrasonic pulse velocity defectoscope.

Construction industry like any other area of economic and social life undergoes continuous alterations and improvements in order to successfully comply with the requirements of sustainable development. Consumers demand more durable, less labour and service intensive materials at a competitive price. To meet these expectations numerous new composite materials have been developed over the last couple of decades, including cementitious materials modified by superabsorbent polymers (SAP). The paper presents part of the larger research project on the performance of cementitious mortars containing two types of superabsorbent polymers (SAP) as the internal curing agent.SAP A is a copolymer of acrylamide and acrylic acid and SAP B is a polymer based on acrylic acid. Research work presented in this paper involves macro and micro scale characterisation of polymer modified mortars. The microstructural features were studied with application of the Mercury Intrusion Porosimetry and the Scanning Electron Microscopy techniques. Analyses of pore size distribution in mortars of different ages are accompanied by the analyses of strength and autogenous shrinkage development as well as early density changes in immature mortars by the X-ray absorption method. The investigations confirmed the positive effect of SAP A on the reduction of autogenous shrinkage and microcrack propagation. Limited absorption/desorption abilities of SAP B cannot reassure continuous supply of water and hence the performance of SAP B mortars was comparable with the reference samples. The effect of both SAPs on strength development proved to be negligible.

This is the third volume published in the series of proceedings of international symposia called 'Brittle Matrix Composites' organised every three years in Poland. The first Symposium, denoted as BMC1, was organised in Jablonna near Warsaw in 1985 under the auspices of the European Mechanics Committee (EUROMECH 204). The second (BMC2) took place in Cedzyna near Kielce in 1988; the present (BMC3) is being held in Warsaw in September 1991. The BMC Symposia are intended to cover mechanical problems related to three main groups of composite materials: high-strength composites, ceramics and cement-based materials. The common feature which is a link between these materials is their brittle behaviour. Brittleness has no clear definition, but it is considered as an important potential disadvantage of every material. Brittle fracture creates various situations which may be very dangerous for the safety and serviceability of structures manufactured from composite materials. Also the brittleness of non-structural elements may give rise to disadvan tageous behaviour, e.g. during transportation and montage. There are many structural and technological ways of reducing material brittleness. Their development and further improvement are of primordial importance for most applications of these composite materials. The problems considered in the series of BMC Symposia cover all aspects of brittle matrix composites: • design studies, theoretical considerations, computational methods; • prediction of behaviour, fracture mechanics and other approaches; • testing methods, test results, all types of experimental studies; • manufacturing processes, applications, observations and durability assess ments, environmental effects, etc.