-
-
-
-
-
In our area, people are discussing the benefits or disadvantages of finishing exterior concrete containing ground granulated blast furnace (GGBF) slag. One group claims that since slag is finer than portland cement, a finisher brings more fines to the surface after straight edge and floating and...
-
-
-
-
-
-
A customer recently divided the placement of a large slab-on-grade warehouse floor into 2 pour days. The plans required the contractor to apply a metallic-aggregate dry-shake hardener. For each pour, a standard 3500-psi concrete mix, without air, was pre-ordered. But on the second day, the crew was...
-
-
-
-
-
-
-
A testing firm employee says concrete should be rejected if the slump exceeds the maximum allowable value by as little as 1/4 inch. Is there any published information to help us argue our case?
-
-
-
-
-
-
-
We supply integrally colored concrete for decorative concrete flatwork in the area. Building owners often complain that the color of the in-place concrete doesn't match that on the color chip supplied by the coloring pigment manufacturer. We then get blamed for not supplying the right concrete. Are...
-
-
-
-
-
We're supplying concrete for a parking deck, to be placed by boom pump. The required air content is 4.5% to 7.5%, and, to account for air lost during pumping, specifications require the test lab to perform air-content tests on concrete sampled from the pump discharge hose. We prefer testing for air...
-
Our customer has asked us to help him evaluate some cracking that occurred on a recent pour of a large parking lot. We believe that the cracks are caused by dry shrinkage, but the owner is concerned that the cracks are structural in nature. We have agreed to monitor the cracks for a year or so to...
-
-
-
-
-
This time of year always brings numerous complaints about driveway wearing surfaces. Conditions that mar a driveway's beauty-and are the homeowner's most common complaint-are popouts and exposed rocks at the slab's surface. More precisely, crushed limestone aggregate is exposed after the medium...
-
-
-
-
-
-
-
-
-
-
-
-
-
We have our plants inspected and certified in accordance with the checklist in Section 3 of the National Ready Mixed Concrete Association's Quality Control Manual. This certification includes truck mixer inspection to ensure that there's no appreciable accumulation of hardened concrete in the drum...
-
When making exposed-aggregate architectural precast channel column covers, we've noticed that after abrasive blasting, the texture on the down face differs from that on the vertical face. What causes this, and what can be done to correct it?
-
What is retarder paper, and how is it used?
-
-
-
-
-
-
-
Your October issue's Troubleshooting question on surface defects prompted this question. In our area, many of the quarries produce coarse aggregate with small percentages of pyrite or marcasite. Once in a while, mineral pieces make their way to the surface. In a short time, there's an ugly rust...
-
-
-
-
-
-
-
-
-
-
-
-
-
-