Practical ultra-high-strength concrete for precast concrete applications

This paper focuses on developing ultra-high-strength concrete (UHSC) with mechanical properties compara­ble to those of ultra-high-performance concrete (UHPC) and with production procedures similar to those used for high-strength concrete. A concrete mixture was developed to achieve a compressive strength of 17 ksi (117 MPa) at 28 days without using silica fume and with a slump flow as high as 35 in. (889 mm). Another concrete mixture with compressive strength of 20 ksi (138 MPa) was designed using only 130 lb/yd3 (77.1 kg/m³) of silica fume. In addition to these two mixtures, a UHPC mixture was also designed with a compressive strength of 24 ksi (165 MPa). Laboratory tests were conducted to investi­gate predictions of modulus of elasticity, flexural strength, creep, and shrinkage for the developed mixtures. This paper demonstrates that using UHSC and 0.7 in. (18 mm) diameter strands will produce adequate flexural strength to design 300 ft (91.4 m) long prestressed concrete I-girders that have service stresses within safe limits