Prevention and Repair of Voids Around Congested Reinforcement


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Title: Prevention and Repair of Voids Around Congested Reinforcement

Author(s): Hrista Stamenkovic

Publication: Journal Proceedings

Volume: 81

Issue: 1

Appears on pages(s): 40-46

Keywords: cements; compressive strength; coarse aggregates; fine aggregates;mortars (material); patching; placing; repairs; reinforced concrete; reinforcing steels; vibration; voids.

Date: 1/1/1984

It may be more appropriate to call cement mortar by the term fine grain concrete. The quality of concrete is not a function of the size of the aggregate but rather a function of the quality of cement mortar or fine grain concrete. If any clearance exists between two adjacent reinforcing bars, it is possible to completely cover and bond the reinforcement in any concrete member by applying two types of concrete: normal concrete with any desired size of gravel and fine grain concrete, where the largest particles are smaller than the clearance between reinforcing bars. By increasing the size of the gravel, the quality (strength) of the concrete is not increased, but the need for the cement mortar in which larger particles of gravel can be immersed is decreased so that for any piece of stone (for a given unit of volume) the smallest possible quantity of cement mortar is required. Consequently, the smaller volume of cement mortar, for a constant quantity of cement, leads to a smaller need for water (as a result of the smaller surface area of sand) and a much higher strength of concrete. By applying two types of concrete (fine and normal) simultaneously, any free space could be-filled between the external form and the congested reinforcement. The practice of applying two types of concrete has been successfully used in Europe for the last 35 years. By vibration of the form, direct vibration of bars, and application of an internal vibrator, it is possible to force out any air and free water, allowing the reinforcement to be totally and fully covered in fresh concrete without air voids, honeycombs, or holes. Two different types of concrete can be prepared with very similar strengths. Ultimate tensile strength is much higher in fine grain concrete in comparison to normal concrete for the same quantity of cement and water. The proportion of sand to cement remains almost identical in both concretes, which will be seen later. Because the fine grain concrete is applied directly between the reinforcing bars, which literally control the shrinkage stresses and shrinkage forces, the two different types of concrete will not be likely to cause cracking. Appendix A gives excerpts from some European standards for consolidation of concrete, indicating that the minimum space (clearance) required is one bar diameter but not less than 3 cm (1.18 in.), conforming closely to AC1 315 and 318.