July 1995 Table of Contents

Features Understanding Specifications for Superflat Floors

There are two basic floor categories: random traffic and defined traffic. Currently, fewer than 1% of the floors constructed in the US are classified as defined traffic. In very-narrow-aisle warehouses, forklifts travel 6-foot wide aisles between storage racks with the aid of rack-mounted rails or a wire guidance system embedded in the floor. While moving down the aisles, these lift trucks can raise their forks to retrieve or place products at various levels. For these forklifts to perform as intended, defined-traffic floors must be extraordinarily flat and level, or superflat. Read more

Features How Mid-range Water Reducers Enhance Concrete Performance

Although mid-range water reducers, like standard water-reducing admixtures, improve concrete strength by reducing the water cement ratio and enhancing hydration, they also provide the following benefits: Read more

Features High-Reactivity Metakaolin

A recent study comparing concrete slabs with and without high-reactivity metakaolin (HRM), a high-performance mineral admixture that yields results comparable to silica fume, found that HRM improves concrete properties while offering good workability and finishability. According to the concrete supplier and contractor involved in the experiment, the non-pozzolanic control concrete and the HRM-modified concrete had similar properties. However, the concrete containing HRM had a creamier texture, set somewhat faster, and generated less bleedwater. Read more

Features Structural Lightweight Aggregate Concrete

With a typical unit weight of 90 to 120 pounds per cubic foot (pcf) and a compressive strength from 2500 psi to more than 8000 psi, structural lightweight concrete is a versatile building material. Since it is generally 20% to 40% lighter than normalweight concrete, a structure's dead load can be reduced, its foundation costs lowered, and its concrete and rebar needs lessened. Structural lightweight concrete also resists fire better than normalweight concrete because of its lower thermal conductivity and its lower coefficient of thermal expansion. In many structures, these benefits justify the use of lightweight aggregate concrete, which generally costs more than normalweight concrete. Read more

Features How Do Admixtures Influence Shrinkage?

The use of admixtures is commonplace in today's concrete mixes. Does the addition of the various admixtures increase or decrease the drying shrinkage of concrete? Does it affect shrinkage at all? These are the questions we asked two distinctly different members of the concrete industry: Ross Martin, vice president of engineering and technical services, Baker Concrete Construction Inc.; and William Phelan, senior vice president of marketing and technical services, the Euclid Chemical Company. Read more

Problem Clinic Use of Shrinkage-Compensating Concrete

We placed an industrial building floor using shrinkage-compensating concrete. This type of concrete was chosen so there would not be as many joints to maintain. Though the floor has very few joints, each joint has opened to a width of nearly 1/2 inch, mak Read more

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