In the second publication in roughly two weeks, following a position statement on project management, the American Society of Concrete Contractors (ASCC) has published another. Marking its 46th, "Water-Cementitious Material Ratio for Concrete to Receive a Trowel Finish" covers the water-cementitious material ratio requirement within the ACI 318-19 Building Code. ASCC Position Statements clarify the concrete contractors’ point of view for architects, engineers, owners, and others.
In their announcement, the ASCC explains:
- The ACI 318-19 Building Code requires a maximum water-cementitious material ratio (w/cm) in accordance with the severity of the anticipated exposure of members, and varies from N/A to 0.55, 0.50, 0.45, and 0.40. Many specifications, however, require a maximum w/cm for interior concrete, often as low as 0.40, which is undesirable for the surface finish.
- ACI 302.2 R-06, “Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials,” recommends a w/cm of 0.50 as the best compromise between drying rate and finishing performance.
- ACI 302.1R-15 “Guide to Floor and Slab Construction” states that specifying a maximum w/cm for concrete workability is not useful, and further recommends a w/cm in the range of 0.47 to 0.55 for concrete floors to receive a trowel finish.
The Position Statement includes additional references from ACI, the National Ready Mixed Concrete Association (NRMCA) and ASTM International.
It recommends that concrete contractors should encourage specifiers to consider ACI 302.1R-15 and ACI 302.2R-06 for w/cm for concrete to receive a trowel finish.
