Design of concrete for moisture-sensitive floorcoverings - Construction Canada

2022-09-17 02:06:08 By : Mr. Lewis Wei

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It takes three to six months for concrete to dry to 70 to75 per cent relative humidity (RH), a safe level to place moisture-sensitive floorcoverings and adhesives. The drying duration, a critical factor in the overall schedule, is directly affected by the concrete mix design, the capillary break and vapour barrier, and curing methods. There are several parties, such as architect/engineer, construction manager, concrete contractor, batch-plant operator, soils/materials testing agency, and floorcovering contractor, each with contractual duties that will affect the successful installation of the floorcovering. While each party has separate duties, no single entity has overall responsibility for the entire process (The term construction manager in this article refers to both construction manager and general contractor (GC). The word architect or architect-engineer refers to both architect and engineer individually. Floorcovering refers to moisture-sensitive floor coverings and adhesives.).

The preconstruction meeting is the opportunity to establish a collaborative working group. The leaders of the meeting (architect/engineer and construction manager) should describe the special challenges of placing concrete for moisture-sensitive floorcovering and reinforce the necessity of each party performing their duties with care. The architect/engineer must play a central role at the meeting because they have the greatest authority to discuss the design and construction documents.

Requirements to be discussed at the meeting include:

The batch-plant operator must also be at the meeting. They must be informed that allowing a driver to add water to the concrete at the site, unless approved by the owner or architect/engineer, could result in the material being sent back to the plant. They should also be reminded to make sure trucks returning from the site are emptied of leftover mix or rinse water.

The principle objectives in planning concrete to receive moisture-sensitive floorcovering are (see the American Concrete Institute’s [ACI’s] 302.1R-06, Guide for Concrete Floor and Slab Construction):

According to the Portland Cement Association (PCA), “all desirable properties of concrete are improved by reducing the total water content to the practical minimum.” A low w/c ratio mix design reduces the delay required to bring the RH of the slab to a safe level to apply the floorcovering and also result in flatter concrete surfaces with less curling and long-term shrink cracking.

The w/c ratio, size, and quantity of coarse aggregate and cement content could affect the total water content. If properly selected, each requirement will result in minimizing the total water content. The w/c ratio is the most important factor when determining the drying rate of a concrete slab. The lower the ratio the faster concrete dries. A plasticizer may be needed to reduce placement difficulties.

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