Issue link: http://digital.canadawide.com/i/755184
DECEMBER 2016 | 19 Concrete including continued shrinkage, traffic loads and thermal cycling. In these slabs, the saw-cut control joint edges require protection to avoid serious spalling and deterio- ration, notes Andy Schultze, marketing manager, VersaFlex Incorporated. "Silicones and polyurethanes make good joint sealants but take at least 24 to 48 hours to fully cure and do not have the shore hardness to be reliable joint fillers," explains Gary Gutierrez, owner of American River Caulking Inc. "Epoxies have the shore hardness to be joint fillers and can cure in four to eight hours, but are not flex- ible or adhesive. They typically crack on both sides of the concrete, debond prema- turely and lack esthetics, and have to be replaced. For new construction, remodels or remediation, we have found that polyureas protect concrete control joints better than epoxies, silicones and urethanes." VersaFlex is a manufacturer of performance formulated polyurea joint filler and sealant. To meet the requirements of a variety of industries, the company provides polyurea systems that are typically hand pumped or dispensed in a range of formu- lations. The polyurea starts to set in about 90 seconds and is tack free in about 10 minutes. The performance formulated polurea has 68 standard colours and hun- dreds of custom colours. VersaFlex also has a concrete repair system called Quick Mender, which has a low viscosity and completely sets in about 10 minutes at 21 degrees Celsius. It can be used to fill holes, spall and popouts, and to repair the broken shoulders of con- trol and construction joints. It adheres to the concrete matrix and fills the capil- laries within the concrete. To increase strength, aggregate or concrete, dust can be added to the Quick Mender slurry. This mix can match the colour of almost any concrete slab. Structural shotcrete has also become a more commonly used concreting method, spreading from the West Coast across Canada. "In traditional concrete construction, we first erect cages of steel reinforcement," notes Roland Heere, senior materials engineer, Metro Testing Laboratories (Burnaby) Ltd. "We then install framework panels on all sides of the component we want to cast, leaving only the top open. We then place concrete into the space between the formwork panels and repeatedly insert vibrators to consolidate the concrete. After the concrete has attained suffi- cient strength to support itself, the formwork is removed. The shotcrete process is similar with two exceptions. First: only one side of a wall requires formwork while the other sides remain open. Second: the concrete is not cast but sprayed with the help of compressed air. The sprayed surfaces are then manually smoothened to achieve an appearance similar to a cast face." Contractors are able to spray apply concrete, rather than cast it, even when con- structing heavily reinforced components designed to withstand severe earthquake loadings, says Heere. Larger-scale structural shotcrete projects are using ready-mix concrete as the main construction material. The concrete mixes are typically designed to achieve nominal compressive strengths in the 40 MPa range. "However, for some highly stressed components, nominal shotcrete strengths may be as high as 60 MPa," says Heere. "The concrete mixes are similar to regular concretes used in form and cast projects. However, shotcrete mixtures are somewhat richer in cement content and sand, while only a small portion of the aggregate is gravel." R I S I N G H I G H When it comes to the concrete market here in Canada, the sector is experiencing an uptick in high-rise concrete construction starts, says Beth Lee, marketing services specialist, Maxxon Corporation. These projects are going up fast, some at the rate of one floor every two days. This rigorous construction schedule puts a tremendous amount of pressure on concrete contractors because of the necessity of meeting specific floor flatness criteria. The SMART (Slab Moisture and Resurfacing Technology) System is an innovative process that originated in Europe and is starting to gain a foothold here in North America. In this system, the concrete contractor is installing the concrete below the specified height. Instead of finishing the concrete, it is left at a rough screed finish. In as little as five days, a surface-applied moisture vapour barrier is installed over the new concrete, preventing the moisture in the still-curing concrete from migrating to the top of the slab. A self-levelling underlayment is then installed over the mois- ture vapour barrier, resulting in a moisture vapour-protected flat floor. "Moisture is released from a concrete slab over weeks or months, and using mechanical dehumidification to accelerate the dry time can cause cracking, curl- ing and physical property loss," says Lee. "Installation of a surface applied mois- ture vapour barrier blocks the movement of moisture vapour through to the top of the slab where it would otherwise collect. Since moisture is prevented from mov- ing through the concrete, adding a surface applied moisture vapour barrier limits the warping and curling of the slab. It also addresses moisture concerns early in the construction process, providing peace of mind that future delays due to moisture emissions have been avoided." LEHIGH HANSON Canada Region affiliated companies Concrete. Cement. Aggregates. Concrete Pipe. LehighHansonCanada.com