Very high early strength of ultra-high performance concrete containing nanoscale pozzolans using the microwave heat curing method

Abstract

This paper deals mainly with the application of a microwave heat curing method to ultra-high strength and performance concrete specimens made up of combinations of micro and nanoscale pozzolans. The application of this curing method enables very high early strength, as high as 420 MPa to be obtained after 1 day by a total microwave curing duration of 2 h. In addition it was observed that the achieved strength depended on the kind of nanoscale pozzolan (oxide) used and on the microwave energy, time of treatment and treatment duration. In comparison with the oven curing method this method has the advantages of much shorter curing times and better curing efficiency. The microwave curing of ultra-high performance concrete seems to be very advantageous for applications where extreme concrete strength in very short time is required. IntroductionUltra-high performance concrete, which is a modern building material with outstanding strength (in excess of 150 MPa), durability and performance, is characterised by a very dense structure and its production is based on the design of composite systems with highly compatible, well graded components. The approach to the production of ultra-high performance concrete (UHPC) makes use of some new processing methods associated with both chemical and physical properties. The processing methods which are related to the chemical properties involve the use of admixtures that reduce the water demand (i.e. superplasticiser polymolecules) and of components (additives) that contribute to an increase in the composite structure density through the production of additional material with very fine porosity (i.e. pozolanically reacting additives). 1-6 The processing methods associated with the physical properties aim to achieve very high density and strength and involve the development of techniques for the designing, casting and curing treatment of the composite. The physical processing methods may be grouped according to the time at which they take part in the action as follows: the pre-mixing processing that is carried out prior to mixing with water (or water and admixtures); the processing during mixing; and the after mixing (post-mixing) processing.The pre-mixing processing comprises among others the selection of raw components, adjusting of their size distributions and of the overall granular grading by making use of models to increase the packing density through mineral blends of different granulometry. 7,8 During examination of the models that aim to increase the packing density, it was found that an extension of the number of granular classes and expansion of the acceptable granular size range by using ultrafine nanoscale additives can lead to an additional increase in the density and considerable improvements to the properties. 9-11 The pre-mixing and processing during mixing together enable the production of concrete with very high strength, durability and performance, 12-14 whereas the post-mixing processing, which can be applied optionally in those cases when extreme properties (i.e....

Microwave processing of cement and concrete materials – towards an industrial reality?

“…The use of a microwave curing method in the production of Ultra High Performance Concrete (UHPC), incorporating so-called nanoscale pozzolans was reported by Korpa and Trettin [44]. While microwave curing resulted in higher strengths, the effect of the microwave curing was not differentiated from that of the nanoscale pozzolans.…”

Natural pozzolans in eco-efficient concrete

“…Improvements in concrete performance have also been sought by resorting to these new disciplines (Korpa and Trettin, 2008;Sanchez and Sobolew, 2010;Cardenas et al, 2011;Nina et al, 2012). One possible application of nanotechnology is the manufacture of nano-pozzolans to raise the reactivity of the original materials.…”