BRINGING HPC FROM LABORATORY TO A PRECAST/PRESTRESSING PLANT

摘要

This paper highlights the difficulties that were experienced in translating high performance concrete (HPC) from laboratory to a precast/prestressing facility. Seven HPC mixtures, first batched in the lab, were selected for trial batching at a plant in Oklahoma. Target compressive strengths were 60 MPa (8,700 psi) at 24 hrs and 100 MPa (14,500 psi) at 28 or 56 days. Three mixture series were evaluated: lab/standard, plant/ambient and plant/heat are distinguished by batching location and curing scheme. Tested at 28 days, the plant-batched mixtures achieved, on average, only 80 % of corresponding lab/standard strengths. Moreover, the plant-batched concrete displayed greater within-test variation at all ages. A chief quality control concern at the plant was regulating the quantity of water in the mixture and batching the concrete as intended. The uncertainty of aggregate moisture made this difficult. Summer temperatures at the plant resulted in diminished workability, as indicated by slump.