Concrete - Division III

1 Cold-weather concreting isn twhat it used to be for AlBrunette, construction man-ager for Dominion Construc-tion Company Limited in are the costly headaches of heatingand conditionsSince turning to chemical admix-tures, Brunette has been able to com-plete winter-condition Concrete jobsfaster, easier and cheaper. Likened to an antifreeze for Concrete , the admixtureprevents the Concrete from freezingwithout the nuisance of supplementaryheat, and enables it to reach full has recently completed twojobs using Pozzutec 20, a chemicaladmixture introduced by The MasterBuilders Company Limited in late than a little impressed by theproduct, he boasts that basically, itgives you summer weather pouring inwinter conditions.

2 No heat or hoardCold weather has often meant delaysfor building contractors. Pouring con-crete required additional time andexpense for hoarding (erecting housingaround newly-poured sections) andConcreteCold WeatherCONCRETINGA new chemical admixture takes the heating and hoarding headaches out ofcold-weather concreting as Dominion Construction erects two Martin BieferAssociate Editorheating to ensure proper curing. Slabsand forms had to be covered withinsulated blankets, but the Concrete stilltook longer to reach full , a veteran of cold-weatherconcreting, has had to rely on heatingand hoarding in past winter jobs. Wintermeans challenges for Dominion, whicherects many of its buildings using the tilt-up method.

3 A slab on grade ispoured first, for the floor. Once the slabhas hardened, forms are laid down onthe slab and the wall panels are , the panels are tilted up, or hoistedinto place. Curing the Concrete quicklyis essential to the strengthDominion first used Pozzutec 20 inNovember when pouring a 2,787 m2slab and corresponding wall panels forthe Palco building in Brampton, Ont.,northwest of Toronto. Temperaturesvaried from 5 degrees Celsius to -4 atnight, recalls Brunette. Normally, fin-ishing within that range of temperatureswould take about 18 hours. At the Brampton site, however, Dom-inton used a mixture of litres ofPozzutec per 100 kg of cement.

4 Withoutheat, hoarding, or insulated blankets, we were able to get on there to float it inabout one hour, says Brunette. Wewalked off, and were able to steel-trowelfinish it in five hours. We didn t have tocover that slab, or protect it eventhough it went down to -4 Celsius thatnight. The addition of Pozzutec 20 enabledDominion to use a high cement mix awater-cement ratio of just .38 and stillget full design strength in 10 days, A Dominion Construction worker spreads Concrete for atilt-up building slab, despite sub-zero cold the mercury dipped, Dominionwent to Pozzutec 20 again for a buildingconstruction project at the corner ofKeele St.

5 And Finch Ave. in was carried out in early Decem-ber, and this time a super-plasticizer,Rheobuild, was also added to the mixat Toronto s Custom Concrete were poured on top of the slabon grade, which was a chilly -2 Concrete was coming in at 17degrees Celsius, and this time litresper 100 kg of cement were used, saysBrunette. As well, an insulating blanketwith an R-4 insulation value was usedto cover the setting panels. Again, no heator hoarding was strengthFor tilt-up construction, strength isessential. At the Keele-Finch job, panelsmeasuring by meters had to behoisted into place. Those are large,heavy panels, notes Brunette, and weneed that 30 MPA strength.

6 Pozzutec 20is perfect in the cold weather, because itgives me the strength I require, with noheat and hoard. With normal cement, the design(strength) on this mix would be 30 MPA(Mega Pascals) in seven days. We needthat strength, because we lift the panelsright away. But here, we were coming inwith strengths of MPA in sevendays. They were unbelievablestrengths. Substantial savingsBrunette calculates his savings at $38per cubic meter for a total of 2,000 estimates he spent between $12 and$13 per cubic meter extra for additives,but saved $50 to $60 per cubic meter onother costs. Normally, I would spend $50 to $60per (cubic) meter to heat and hoardthese.

7 I save material, heat and hoard,and labour, which all comes to about$50 a meter. That s a savings of $38 permeter a substantial amount of mon-ey. Structural applicationsBrunette is already looking to Pozzu-tec 20 for his next winter pouring job. Now that I m getting such highstrengths, I m looking at cutting back onmy cement content and saving evenmore money. Master Builders John Smolyn saysthe work carried out by Dominion represents the greatest exposure, so far,in this area for Pozzutec 20. While theproduct was used in a parking lot projectin Brampton last spring, the work byDominion represents the first structuraljobs carried out with Pozzutec 20 inOntario.

8 The product has seen limiteduse in other parts of the claims the addition of Pozzu-tec 20 to cement mix (it can be added atthe mixing plant) yields Concrete withthree-day strengths of 20 to 23 a super plasticizer like Rheobuildis added, he adds, strengths jump up byanother 15 to 20 MPA. Non-chloride productStrength gain is essential for contrac-tors, says Don Lamb, an engineer forMaster Builders. If strength gain isslower, he can t go on to his next step inconstruction, whether it be flying theform, or doing the tilt up, or whatever itis and that creates problems. Another plus for Pozzutec is that it is anon-chloride admixture, says Smolyn.

9 A lot of engineers, developers andowners do not want calcium chlorideused in their Concrete now, because ofthe oxidization. The MTC (OntarioMinistry of Transportation and Com-munications) won t allow chloride,structural engineers won t allow chlo-ride. Calcium chloride is taboo withengineers today. Bottom lineWhile there are other non-chlorideaccelerators available, Smolyn says Poz-zutec 20 is the only product that will, ifyou use enough, prevent Concrete fromfreezing down to -7 degrees Builders guarantees Pozzutec sperformance down to that admixture will not preventconcrete from freezing unless therequired dosage of to litres per100 kg is used, notes Lamb.

10 The productcosts about $ to $ per for Brunette, the cost of theadmixture is a small price to pay. Thebottom line, he says, is that Pozzutec 20takes the chill out of winter concretework. We re definitely sold on it, there s noquestion. We ll be using it in thisindustry as long as we can and in anyapplication we can. Use of a chemical admixture, Pozzutec 20, enables Dominion Construction crews to pour Concrete despite winterconditions. The chemical enables pouring in temperatures down to -7 degrees from CANADIAN CONSTRUCTION RECORD/February 1988 issu