Car park structures When the cold sets in Dr Steven Holmes, senior technical manager at Sika, explains the limitations of traditional cement-based materials and how materials with alternative technologies can be used to repair and strengthen car park structures, even when the temperatures plummet ulti-storey car parks (MSCPs) almost always feel colder than the temperature reading in your car would suggest: a welcome retreat in summer, but less so in winter. Repair and refurbishment of our MSCPs often continues apace through the winter, so understanding the limitations of the materials we apply to them when it comes to temperature is critical if we are to achieve the aims of structural refurbishment and maintenance. M The scenario Its the night shift on a winters night, and you have placed rapid-set concrete repair materials to your car park, which should allow you to re-open to the paying public first thing in the morning. The problem is, youre not convinced the flowable mortar you poured is going to be ready to receive traffic in just a few hours. As morning approaches, you have to make a decision keep the deck closed for a few hours to allow the material to reach strength, with the potential loss of revenue this brings, or open up and risk further damage. Neither eventuality is good, because if the temperature was too low for the repair material on application, it may never perform as specified and fail prematurely, and youll be digging everything out and starting again most likely at your own cost. Why it happened It may be that programme delays pushed the project into the winter months, so products that were specified for summer or autumn conditions were used. There may have been a misunderstanding about the materials properties were all human after all or an attitude from operatives of weve used this in winter before and it was fine. The risk is that the applied material will never achieve the properties stated on the data sheet. 30 If you are working on an MSCP project in low temperatures out of necessity, and require products that will allow you to progress whatever the weather, and that give you a quick return to service, there are products specially formulated for this purpose. Technologies for low temperatures All of the technologies used to formulate products that can be used in low temperatures still rely on a series of chemical reactions to gain strength and achieve the material properties required. The difference between traditional cementitious products and the more modern materials below is that the rate of these reactions at low temperatures allows them to reach their stated material properties often very quickly and, in some instances, at temperatures as low as -20C. Alternative solutions include: Magnesium phosphate cement a blend of magnesium oxide and ammonium dihydrogen phosphate that reacts with water to rapidly produce heat and strength, significantly quicker than most ordinary Portland cement-based products. Polymethyl methacrylate (PMMA) a thermoplastic resin requiring an activator to catalyse, it is rapid curing, often achieving full cure in an hour. As it doesnt contain water, it is ideal for use in low temperatures. Polyurethane methacrylate (PUMA) rapid curing and requires a catalyst. Unlike traditional materials, but similar to PMMA, the formation of bonds at the molecular level is unaffected by time, making it extremely durable. PUMA products display elongation properties, making them useful for crack bridging, even at very low temperatures. Reactive acrylic resins when combined with a catalyst they have accelerated chemical reaction rates, generating significant heat and therefore allowing them to be used in very low temperatures. The curing