June 1997 Table of Contents

Features Take the Sweat Out of Hot-Weather Concreting

Hot weather can have many negative effects on fresh and hardened concrete properties, including increased water demand, accelerated rate of cement hydration, increased moisture and slump loss, faster setting times, increased plastic- and drying-shrinkage cracking, and lower ultimate strengths. But construction doesn't have to stop when air temperatures rise above 90øF. By adding chemical admixtures to concrete mixes, you can improve concrete workability while reducing total water content. Other benefits included increased concrete strength and durability and lower total in-place costs. Read more

Features Curing During the Pour

An early start on concrete curing can provide many benefits, especially for hot-weather placements. It can help to prevent stickiness, sponginess and surface crusting conditions that can cause finishing problems. It can also eliminate plastic shrinkage cracking and reduce drying shrinkage cracking. In hot weather, many contractors cure concrete between bull floating and power floating. For large concrete pours, curing may also be needed between screeding and bull floating and between floating and troweling passes. Read more

Features Keep Your Cover with Side Form Spacers

If you're a concrete contractor, it's important that you maintain adequate clear cover in vertical concrete structures. With proper cover, reinforced-concrete structures are likely to exhibit improved structural integrity and finished appearance as well as greater resistance to fire and corrosion. Without it, the reinforcement is vulnerable to corrosion and the concrete to early deterioration. Though designers specify clear cover for vertical formed surfaces, they seldom specify the means for maintaining it. That's the contractor's responsibility. Read more

Features The Impact of Metric Rebar Conversion

Because federally funded construction projects are now required to be designed in metric units and built with metric materials, mills are reducing and will eventually eliminate their output of inch-pound bars and produce soft metric bars instead. Fortunately, the use of soft metric rebar will not require changes in design or in fabrication and construction practices, since soft metric rebar are physically the same size as corresponding inch-pound bars. It will be important, however, for designers and contractors to become familiar with the specifications of the new metric bar sizes. Read more

Features Getting the Curves Straight

From the street, it appears that the glass facade of the new Rio Suites Hotel, Las Vegas, wraps around the curved building like smooth cellophane. But the "curved" edge of each floor slab actually is segmented to fit the flat panes of glass. Had just one of these segments on a single floor been cast incorrectly, the glass would not have fit. Read more

Problem Clinic Required Joint Depth for Early-Cut Saws

We used an early-cut saw to joint a concrete floor immediately after finishing. The floor is 6 inches thick and the sawcut depth is 3/4 inch. Although the floor has no random cracks, the engineer says we now have to chase the joints with a conventional sa Read more

Problem Clinic Can Acid Cleaning Cause Driveway Deterioration?

I run a pressure-washing business in Georgia. To remove the red clay that stains many driveways, I wet the driveway, then use a low-pressure hand sprayer to apply a dilute solution of muriatic acid (one part commercial-grade muriatic acid to three parts w Read more

Problem Clinic There Are Thickness Tolerances for Driveways

Questions such as the one in the March 1997 Problem Clinic (p. 313), where a reader asks if there is a published thickness tolerance for residential driveways, bring out the importance of placing important construction parameters in easily accessible form Read more

Problem Clinic Cast Stone Differs From Precast Concrete

What is the difference between cast stone and precast concrete? Or is there a difference? Read more

Close X