NCMA TEK

1 ncma TEKN ational Concrete Masonry Associationan information series from the national authority on concrete masonry technologyTEK 3-1 CConstruction (2002)ALL-WEATHER CONCRETEMASONRY CONSTRUCTIONINTRODUCTIONM asonry construction can continue during hot, cold, andwet weather conditions. The ability to continue masonry con-struction in adverse weather conditions requires considerationof how environmental conditions may affect the quality of thefinished masonry. In some cases, environmental conditionsmay warrant the use of special construction procedures to ensurethat the masonry work is not adversely of the prerequisites of successful all-weather construc-tion is advance knowledge of local conditions. Work stoppagemay be justified if a short period of very cold or very hot weatheris anticipated. The best source for this type of information is Weather Bureau, Environmental Science Services Admin-istration (ESSA) of the Department of Commerce whichcan be accessed at their web site the following discussion, ambient temperature refers tothe surrounding jobsite temperature when the preparationactivities and construction are in progress.

2 Similarly the meandaily temperature is the average of the hourly temperaturesforecast by the local weather bureau over a 24 hour periodfollowing the onset of construction. Minimum daily tempera-ture is the lowest temperature expected during the between 40 and 90oF ( and ) areconsidered normal temperatures for masonry constructionand therefore do not require special procedures or WEATHER CONSTRUCTIONWhen ambient temperatures fall below 40oF ( ), theSpecification for Masonry Structures (ref. 3) requires consider-ation of special construction procedures to help ensure the finalconstruction is not adversely affected. Similarly when theminimum daily temperature for grouted masonry or the meantemperature for ungrouted masonry falls below 40oF ( )during the first 48 or 24 hours after construction respectively,special protection considerations are : cold weather construction, construction tech-niques, grout, hot weather construction, mortar, rain, snow,storage of materials, wet weather construction, windyweather constructionMortar and Grout PerformanceHydration and strength development in mortar and groutgenerally occurs at temperatures above 40oF ( ) and onlywhen sufficient water is available.

3 However, masonry construc-tion may proceed when temperatures are below 40oF ( )provided cold weather construction and protection require-ments of reference 3 are and grouts mixed at low temperatures have longersetting and hardening times, and lower early strength than thosemixed at normal temperatures. However, mortars and groutsproduced with heated materials exhibit performance character-istics identical to those produced during warm of FreezingThe initial water content of mortar can be a significantcontributing factor to the resulting properties and perfor-mance of mortar, affecting workability, bond, compressivestrength, and susceptibility to freezing. Research has showna resulting disruptive expansion effect on the cement-aggre-gate matrix when fresh mortars with water contents in excessof 8 %mortar are frozen (ref.)

4 2). This disruptive effectincreases as the water content increases. Therefore, mortarshould not be allowed to freeze until the mortar water contentis reduced from the initial 11% to 16% range to a value below6%. Dry concrete masonry units have a demonstrated capac-ity to achieve this moisture reduction in a relatively shorttime. It is for this reason that the specification requiresprotection from freezing of mortar for only the first 24 hours(ref. 3).Grout is a close relative of mortar in composition andperformance characteristics. During cold weather, however,more attention must be directed toward the protection of groutbecause of the higher water content and resulting disruptiveexpansion that can occur from freezing of that water. Therefore,grouted masonry needs to be protected for longer periods toallow the water content to be cold weather masonry construction, Type III, high-early strength portland cement should be considered in lieu ofType I portland cement in mortar or grout to accelerate acceleration not only reduces the curing time but generatesmore heat which is beneficial in cold 3-1C 2002 national Concrete Masonry Association (replaces TEK 3-1B)from precipitation and ground water by storage on pallets or otheracceptable for materials include tarpaulins, reinforced paper,polyethylene, or other water repellent sheet materials.

5 If the weatherand size of the project warrant, a shelter may be provided for thematerial storage and mortar mixing HeatingWhen the ambient temperature falls below 40 F ( C)during construction, or mean daily temperature is predicted to fallbelow 40 F ( C) during the first 24 hours following constructionof ungrouted masonry, or the minimum daily temperature ispredicted to fall below 40 F ( C) during the first 48 hours forgrouted masonry, Specification for Masonry Structures (ref. 3)requires specific construction and protection procedures to beimplemented as summarized in Tables 1a and 1b. As indicated inAdmixturesThe purpose of an accelerating type of admixture is tohasten the hydration of the portland cement in mortar or , admixtures containing chlorides in excess of ions are not permitted to be used in mortar (ref.)

6 3) due tocorrosion of embedded metals and contribution to specifically not addressed by the Specification, the use ofchloride admixtures in grout is generally accelerators are available but they must be used inaddition to cold weather procedures and not as a replacement forthem. Antifreezes are not recommended for use in mortars and areprohibited for use in StorageConstruction materials should be protected from water bycovering. Bagged materials and masonry units should be protectedTable 1a Cold Weather Masonry Construction Requirements (ref. 3) Ambient temperatureConstruction requirementsDo not lay masonry units having a temperature below 20oF ( ). Remove visible snow and iceon masonry units before the unit is laid in the masonry. Remove snow and ice from existing foundation and masonry surfaces to receive new masonry above freezing.

7 Heatmixing water or sand to produce mortar temperatures between 40 and 120oF ( and ).Grout materials to be 32oF (0oC) minimum. Do not heat water or aggregates above 140oF (60oC).Same as above for mortar. Maintain mortar temperature above freezing until used in grout aggregates and mixing water to produce grout temperatures between 70 and 120oF ( ). Maintain grout temperature above 70oF ( ) at time of grout as above, plus use heat masonry surfaces under construction to 40oF ( ) and install windbreaks or enclosures when wind velocity exceeds 15 mph (24 km/hr). Heat masonry to a minimumof 40oF ( ) prior to as above, plus provide an enclosure for the masonry under construction and use heat sourcesto maintain temperatures above 32oF (0oC) within the to 40oF (0 to )25 to 32oF ( to 0oC)20 to 25oF ( to )20oF ( )and belowTable 1b Cold Weather Masonry Protection Requirements (ref.)

8 3)Protection requirementsProtect completed masonry from rain or snow by covering with a weather-resistivemembrane for 24 hours after cover the completed masonry with a weather-resistive insulating blanketor equal for 24 hours after construction (48 hr for grouted masonry unless only TypeIII portland cement used in grout).Maintain masonry temperature above 32oF (0oC) for 24 hours after construction byenclosure with supplementary heat, by electric heating blankets, by infrared heatlamps, or by other acceptable methods. Extend time to 48 hours for grouted masonryunless the only cement in the grout is Type III portland daily temperature forungrouted masonryMinimum daily temperaturefor grouted masonry25 to 40oF ( to )20 to 25oF ( to )20oF ( )and belowTable 2a Hot Weather Masonry Preparation and Construction Requirements (ref.

9 3)AmbienttemperaturePreparation and construction requirementsAbove 100oF ( ) orMaintain sand piles in a damp, loose condition. Maintain temperature of mortar and grout above 90oF ( )below 120oF ( ). Flush mixer, mortar transport container, and mortar boards withwith a wind speed greatercool water before they come into contact with mortar ingredients or mortar. Maintainthan 8 mph ( km/hr)mortar consistency by retempering with cool water. Use mortar within 2 hours of 115oF ( ) orSame as above, plus materials and mixing equipment are to be shaded from direct 105oF ( )Use cool mixing water for mortar and grout. Ice is permitted in the mixing water as long aswith a wind speed greaterit is melted when added to the other mortar or grout 8 mph ( km/hr)Table 2b Hot Weather Masonry Protection Requirements (ref.

10 3)Mean dailytemperatureProtection requirementsAbove 100oF ( ) orFog spray all newly constructed masonry until damp, at least three times a day until the above 90oF ( )masonry is three days a wind speed greaterthan 8 mph ( km/hr)Table 1a, the temperature of dry masonry units may be as low as 20oF( ) at the time of placement. However, wet frozen masonryunits should be thawed before placement in the masonry. Also, evenwhen the temperature of dry units approaches the 20oF ( )threshold, it may be advantageous to heat the units for greater should never be placed on a snow or ice-coveredsurface. Movement occurring when the base thaws will cause cracksin the masonry. Furthermore, the bond between the mortar and thesupporting surface will be Unit MasonryFor glass unit masonry, both the ambient temperature and the unittemperature must be above 40oF ( ) and maintained above thattemperature for the first 48 hours (ref.