October 2000 Table of Contents

Features Concrete Market Y2K

More than 441 million cubic yards of concrete will be placed in 2000. And the total in-place concrete cost? A whopping $88 billion dollars. That's up almost 13% from 1999. We gathered cement and concrete statistical data from several sources. Then, with the help of the Portland Cement Association and R.S. Means, a company specializing in estimating and analyzing construction costs, we developed a methodology for estimating the total dollar value of cast-in-place concrete. We extended the methodology to estimate the amount of concrete placed in various building elements, including footings, walls, slabs on grade, columns, and elevated slabs. Read more

Features Quick Fix

To minimize traffic interruptions and speed construction on road and runway rehabilitation projects, Caltrans and other transportation agencies are using rapid-hardening-cement concrete (RHCC). Although similar to portland cement in many ways, rapid-hardening cement has a different chemistry, giving concrete significantly improved properties. RHCC with a 5-inch slump and 650 pounds of cement per cubic yard routinely achieves compressive strengths of 2500 to 3000 psi in 1 1/2 hours. Its shrinkage is about 25% that of portland-cement concrete (PCC) of the same slump, and its porosity is much lower, contributing to improved durability. In freeze/thaw tests (ASTM C 666), RHCC can withstand 1000 freeze/thaw cycles, compared with only 350 cycles for most PCCs. Generally, rapid-hardening cement can be substituted pound for pound for portland cement. Mixing and placing procedures for RHCC and PCC also are similar. Read more

Features First-Aid Kits for Concrete

The truck mixer has moved into position on your jobsite and begins discharging concrete. With a quick field test, you determine that the concrete isn't suitable for the intended use. Fortunately, contractors may be able to fix some concrete mixes onsite by using water reducers and other admixtures available in preweighed portions. Packaged in bags, the admixtures can be conveniently tossed into the truck mixer, eliminating spillage and waste. Read more

Features End-of-the-Year Rush

For many concrete contractors, it seems that all projects taking placing in late fall end up being "rush" jobs to beat the cold weather. But even contractors who don't work in areas with the potential for bad winter weather find that jobs get pushed and squeezed at the end of the year. Some projects are budgeted to be completed by year-end, so customers press their contractors to finish on schedule. The need to occupy building, retail, or parking space can also push a customer's hot button. Read more

Features Shotcrete Core Grading: Is It Working?

When ACI 506.2-95, "Specifications for Materials, Proportioning, and Application of Shotcrete," was adopted in 1995, one of the most controversial sections required a visual core-grading system for evaluating reinforcement encasement. Five grades were established, with grade 1 indicating the highest quality and grade 5 the lowest. Read more

Features Troubleshooting: Popouts

Popouts are pits left in the concrete surface after concrete has broken away due to localized internal pressure. Most often, they are caused by pieces of porous rock, such as chert, weathered dolomite, or shale, that are highly absorptive and have a relatively low specific gravity. If these aggregates become saturated and freeze, they either fracture due to internal pressure or push enough water into the mortar cover to cause the mortar to pop off. Popouts typically range from about 1/4 inch to several inches in diameter, and usually a portion of or all of the aggregate that caused the popout remains at the bottom of the hole. Read more

Decorative Concrete Engraving Concrete

Property owners often assume that their old, plain-concrete pavements or floors have little aesthetic value. However, various engraving tools and equipment are now available to allow contractors to convert plain-concrete surfaces into interesting decorative finishes that will greatly enhance the beauty of existing hardscapes. Engraving concrete involves the use of diamond cutting tools to produce repetitive patterns or one-of-a-kind graphics. Some decorative-concrete contractors even create freehand images using angle grinders or engraving pens. Introducing color completes the look. Read more

Problem Clinic Acceptable Curling

Are there any standards for an acceptable amount of curling for a concrete floor slab? Read more

Problem Clinic Crack Coverup

The concrete subcontractor who placed some sidewalks for us didn't cut any joints, so there are meandering cracks in the sidewalk. Does any company make expansion-joint covers for this application? Read more

Problem Clinic Who Places Vapor Retarder?

When specifications call for a vapor retarder beneath a concrete floor, what subcontractor normally is responsible for putting the vapor retarder between the base course and the concrete slab? Read more

Problem Clinic Sources for FRP Rebar

We have a job that requires us to use fiber-reinforced polymer rebar. Where can we purchase this material? Read more

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