Material and environmental factors influencing the compressive strength of unsealed cement paste and concrete at high temperatures

Results of uniaxial compressive strength measurements taken on 1210 unsealed cement paste and concrete specimens heated to temperatures up to 600°C are reported; they show that both material and environmental factors have a significant influence during the heat cycle and afer cooling. The best results were obtained using firebrick aggregate and a cement blend containing 65 % slag replacement of OPC by weight. At 600°C the “hot” compressive strength of this material was 85% of the value measured before heating.