Concrete… maintaining the Quality Achieving durable exterior flatwork in residential construction

Objectives Review the exterior flatwork problem we face Discuss the issues with achieving durable exterior flatwork Technical summary What can the homebuilding industry do?

Residential Exterior Flatwork Concrete work subcontracted to a finishing company Exterior concrete looks great when home is turned over Homebuilder hears from unhappy home owner after 1 st or 2 nd winter What is the problem? What caused it? Who is responsible?

What it looks like…

What causes it… Inadequate or no curing and/or Inappropriate finishing and/or Inappropriate concrete and/or Incorrect or no sealing & maintenance In combination with exposure to freezing temperatures & water (& de-icing chemicals)

What do we do? Must treat achieving durable exterior flatwork as a chain of important events Each link must be executed correctly to prevent deterioration Industry partners must work together Suppliers cannot make a bullet proof concrete

Achieving Durable Exterior Flatwork…Technical Review Concrete Placing Finishing Curing Sealing & Maintenance

Concrete Alberta Building Code & Canadian Standards Association require: C-2 Exposure (de-icing chemicals & freeze/thaw) 32MPa (or 30MPa where indigenous aggregates do not achieve 32MPa) 0.45 w/cm 5-8% fresh air (3% hardened air with spacing factor not exceeding 0.23mm) ARMCA Recommends DURA-MIX above requirements and; 300kg/m 3 of cement minimum

Placing Subgrade should be dampened and not frozen For more consistent set and improved workability CSA A23.1 requires concrete to be placed within 120 minutes from batching Prolonged mixing results in loss of air, slump & compressive strength Water should not be added to increase slump above 100mm Additional water significantly reduces freeze thaw resistance Slump over 100mm should be achieved with a high range water reducer (superplasticizer)

Finishing Minimize handling and do not over vibrate Allow bleed water to evaporate before finishing Do not use steel trowels (Fresno) or power trowels on air entrained concrete CSA A23.1 Steel trowel finish should not be applied to air-entrained concrete Blistering or scaling might occur if trowel finish is applied Use a magnesium float and concrete broom

Curing Essential for surface durability! Must balance 3 critical elements TimeTemperatureMoisture

Methods of curing There are two ways to cure concrete: 1) add water to the surface to replace the water that is evaporating 2) seal the concrete to prevent the water from evaporating Note: adding water to the surface is NOT adding water that will be worked into the concrete mix--that would weaken it. Wet Curing Blankets Ponding Method Liquid Curing Membrane

CSA Curing –Table 20 A wet-curing period of 7 d. The curing types allowed are ponding, continuous sprinkling, absorptive mat or fabric kept continuously wet. Extended3 7 d at > 10 °C and for a time necessary to attain 70% of specified strength. When using silica fume concrete additional curing procedures shall be used See Clause Additional2 Description 3 d at > 10 °C or for a time necessary to attain 40% of specified strength Name Basic Level 1 6/13/ Note (2) recommends concrete be allowed to air dry for at least one month after curing before exposure to de-icing chemicals C-2 Exposure requires Level 2 curing

Hot Weather/Severe Drying When surface evaporation is more than 0.50kg/(m2/h) the concrete must be protected Hot temperatures &/or windy low relative humidity Evaporation retardant (Confilm, Profilm etc) is recommended Apply as soon as possible Do not use as a finishing aid

High Evaporation Days ARMCA website has a tool to calculate evaporation rate Input values: concrete temperature, air temperature, relative humidity and wind velocity July & September 2011, # of days where protection was required Calgary:July – 29 : Sept – 24 Red Deer:July – 20 : Sept – 23 Edmonton:July – 20 : Sept – 26

Cold Weather Concrete must not freeze before it has reached 3.5MPa! Concrete needs a significant portion of design strength to withstanding freeze thaw cycles Concrete must be allowed to dry out & mature before first winter Use of winter heat (warm concrete & accelerators) does not replace required curing

Cold Weather Construction Local municipalities require cold weather construction practices for pavement placed after September 30 th CSA A23.1 Level 2 curing required 7 days at a minimum of 10 °C or the time required to attain 70% of 28 day strength

Impact of Temperature on Concrete 6/13/201420

Long Term Strength Development 6/13/201421

Sealing & Maintenance Properly seal the concrete 28 days after concrete placement & before exposure to traffic Penetrating sealers (silane or siloxane) are recommended and should be reapplied at least every 3yrs Concrete placed after Sept 15 should be sealed the following spring Concrete should be cleaned yearly Snow and ice should be removed as it accumulates

De-icing Chemicals Avoid whenever possible All increase the number of freeze thaw cycles & some attack the concrete matrix Especially damaging in the first winter when concrete hasnt reached its full strength Sand is the recommended product to improve traction on ice Most of the de-icing chemicals present on driveways come from tire transfer from city roads If all the links in the chain are executed correctly exterior flatwork can withstand exposure to standard de-icing chemicals

Achieving Durable Exterior Flatwork…Homebuilder Influence Insist on DURA-MIX & test concrete before placing Insist on certified journeyman finishers Insist finishers use appropriate curing methods for the environmental conditions Provide home owners with the appropriate information regarding sealing & maintenance

The Challenge… This or 6/13/ After 1 year of strengthening the links in the chain do you have:

Questions?

ARMCA Residential Committee Committee reinstated in 2011 Looking for more representation Home Builders Finishers If interested contact Ed ARMCA