Masonry Magazine August 1976 Page. 11
BIA Technical Notes on Brick Construction
Brick Institute of America 1750 Old Meadow Road, Mclean, Virginia 22101
8
REVISED
Sept.
1972
INTRODUCTION
PORTLAND CEMENT-LIME MORTARS FOR BRICK MASONRY
Mortar is the bonding agent that integrates a masonry wall. It must be strong, durable, capable of keeping the wall intact, and it must create a water-resistant barrier.
Because portland cement concretes and masonry mortars contain the same principal ingredients, some designers assume that what is good practice for concrete will also be good practice for mortars. In reality, mortars differ from concrete in working consistencies, in methods of placement, and in the structural elements which utilize each. Mortar binds structural masonry units into a single element, while concrete is usually a structural element in itself. With portland cement concrete, most of the important physical properties are strength characteristics, usually functions of its compressive strength. The principal function of masonry mortars is to develop a complete, strong and durable bond with masonry units. For these reasons the requirements for masonry mortars are vastly different from those for portland cement concretes.
COMPOSITION AND PROPORTIONS
General. For many years, the principal mortar constituents have been portland cement, lime, sand and water. This Technical Notes and Technical Notes 8A concern themselves with mortars containing only those ingredients. Each material makes a definite contribution to mortar performance. Portland cement, a hydraulic cement, contributes to durability, high early strength and high compressive strength. Lime, which sets only upon contact with air, contributes to workability, water retentivity and elasticity. Both contribute to bond strength. Sand acts as a filler, providing the most economic mix and contributing to strength. And water is the mixing vehicle which creates plastic workability and initiates the cementing action.
Because lime hardens only upon contact with air, it is likely that complete hardening occurs very slowly over a long period of time. This fact will lead to healing, the recementing of small hairline cracks. Healing will tend to keep water penetration to a minimum.
The discussions of Materials and Proportions that follow are based on the Standard Specification for Portland Cement-Lime Mortar for Brick Masonry, BIA-M1-72, that appears in Technical Notes 8A.
Materials. Standard BIA-M1-72 contains a list of acceptable mortar materials and the ASTM Standard governing each. Comments pertaining to these materials follow.
Portland Cement. Portland cement, a hydraulic cement, is the principal cementitious ingredient for the mortars covered by BIA-M1-72. Only three of the eight types covered by ASTM C 150, Standard Specifications for Portland Cement, are recommended. They are:
Type I-For general use when the special properties of Types II and III are not required.
Type II-For use when moderate sulfate resistance or moderate heat of hydration is desired.
Type III-For use when high early strength is desired.
Because air entrainment has the definite, detrimental effect of reducing bond between mortar and masonry units or reinforcement, the use of air-entraining portland cements (Types IA, IIA or IIIA) is not recommended.
Also, since the allowable stresses for the structural design of brick masonry are based exclusively on the results of extensive tests in which only portland cement-lime mortars were used, the use of such blended hydraulic cements as portland blast-furnace slag cement, portland pozzolan cement and slag cement (Types IS, IP and S of ASTM C 596, Standard Specifications for Blended Hydraulic Cements) is not recommended in mortar unless the strengths of masonry constructed with mortar containing such cements are first established by appropriate tests. This is not to say, however, that for non-structural masonry such blended cements cannot be substituted for regular portland cements without the necessity of such prior testing.
Natural cements are not recommended for use in masonry mortars.
Hydrated Lime. Hydrated lime is quicklime which has been slaked before packaging, converting