Physical and mechanical properties of Ultra-high- performance concrete with limestone

The production of ultra-high performance concrete is one of the new ideas in modern construction, developed in the past few decades. A compressive strength higher than 150 MPa has been achieved using a relatively large amount of cement, approximately 800 kg/m3. As the cement industry is one of the largest producers of carbon dioxide, it is clear that the cement amount in concrete should be reduced to minimize greenhouse gases emission and slow down the global warming process. One possibility for that reduction is a replacement of cement with limestone filler. This paper shows the results of experimental testing of five ultra-high-performance concrete mixtures. A referent mixture and four mixtures with a partial replacement of cement with limestone filler were made and tested. Two types of limestone fillers varying in particle size were used: one with a mean particle size of 2.5 μm and the other one with a mean particle size of 11 μm. Two groups of concrete mixtures were made with 20% and 30% of cement replaced by limestone. All other components: silica fume, quartz sand, water and superplasticizer were kept constant in all mixtures. Limestone filler is selected based on a particle size - so that its particles are the same size or smaller compared to cement. Basic fresh and hardened concrete properties were tested for all mixtures: consistency was determined using standard flow test and 28-day compressive strength was obtained by testing 10-cm cube samples. Based on the obtained results, it could be concluded that the replacement of cement with limestone brought improvements in compressive strength and workability. The compressive strength of all mixtures was app. 120 MPa, while the mixtures with limestone were more flowable. The economic aspect was also considered. The analysis showed that up to 25% cost reduction can be achieved without compromising the compressive strength of this type of concrete by using limestone as a filler