Soaring to a record height of 91 feet, 7 ¼ inches, two tilt-up concrete wall panels were used by Gloria Dei Lutheran Church, Nassau Bay, Texas, to frame the 117-foot-tall cross for the church's new worship center. Though standard procedures were used to form and cast the panels, their enormous size and heft called for carefully engineered rigging and bracing. Each panel weighed 163,300 pounds and required approximately 41 cubic yards of concrete. Read more
The final part of a three-part series, this article discusses the role top-down stiffening of concrete plays in delaminations. Concrete gradually stiffens, or loses plasticity, as water is lost and hydration products build up. Although a small amount of water immediately combines with cement during the first few minutes of mixing, most of it remains uncombined as hydration reactions enter a dormant period. During this dormant period, the stiffening rate is less affected by hydration-product buildup than by water loss. Thus, for most slabs, timing of finishing operations may depend more on jobsite factors affecting water loss. Read more
Article describes a portable, hydraulic-powered tool that can produce 90-, 135- and 180-degree bends in seconds in in-place rebar, after the concrete is poured. One worker reportedly can make up to 800 bends in just one day. Not only does the tool save time and labor, it reduces the risk of injury associated with manual bending and the need for costly splices, couplers and welds. Read more
A growing number of concrete foundation contractors are saving time and labor and improving layout accuracy by using robotic surveying instruments to do one-person foundation layouts. One such system--the Geodimeter 600, from Spectra-Precision Surveying Inc., Itasca, Ill.,--consists of an unmanned robotic total station, which is operated from the measuring point, and a remote positioning unit (RPU). The unmanned total station has a built-in tracking module that automatically searches for and locks onto a target on the RPU as the operator moves the RPU rod from survey point to survey point. This automatic tracking greatly reduces surveying time because the operator doesn't have to manually aim and focus. It also can eliminate the risk of compounded errors, which can occur when incorrect points are used as references for the points that follow. Read more
Article describes a cast-in-place concrete wall system that delivers the beauty of stone at a fraction of the cost. The patented wall system uses form liners molded from natural rock surfaces to produce a deep-relief pattern in concrete that replicates an actual stone-and-mortar wall. Available in a variety of patterns, the liners can be bolted onto standard concrete wall forms and are made of a durable urethane that provides multiple reuses. The liners come in a 2x6-foot size for straight walls and in various corner, post and filler sizes. For easier stripping, the liners can be coated with a nonstaining release agent. Read more
Article describes a new spray-applied solution for skin that neutralizes the irritating effects of wet concrete. Manufactured by Force Field Technologies Inc., Fort Worth, Texas, the solution is formulated to control chronic and allergic dermatitis by acting as a topical skin buffer and neutralizer. Tests show that it neutralizes the high pH, or alkalinity, on skin that has been in contact with wet concrete and reduces hexavalent chromium (a chemical in cement that causes allergic contact dermatitis) to undetectable levels. Read more
Our placing crew splattered concrete on an aluminum storm door when we were placing a patio. Read more
We placed a concrete wall for which the architect wanted an exceptionally smooth surface on the top 2 to 3 feet. We formed most of the wall with standard steel-faced forms but used hardboard at the top. When we removed the forms, the concrete surface in c Read more
Is it necessary to use a curing compound when a concrete slab is placed during the spring or fall and temperatures approach 60ºF during the day but are sometimes below freezing at night? Read more
Do you have any suggestions for removing rubber tire marks from precast concrete pavers? Read more
We've seen several references to a concrete-cleaning device that removes elastomeric membranes, paints and coatings by flame blasting. Oxygen and acetylene are combined to produce a flame that is passed at a given height and rate over the substrate. This Read more