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  • Suresh Kumar

Physical Properties of Lime Mortar

Updated: Dec 5, 2019

The lime mortars have been used for more than thousands of years to build ancient buildings, pyramids, massive walls, palaces, and small structures. In 1920, the invention and development of Portland cement dwindled lime mortar utilization in building construction. Because lime mortar does not dry out too quickly that takes more time to set but Portland cement set instantly. Nonetheless, Portland cement can’t replace the lime mortar traits which are invincible in making massive structures. Since the importance of lime mortar widely known by engineers, architects, and inhabitants who are willing to build eco-friendly lime mortar houses again. Lime mortar physical properties are determined by their workability or plasticity, water retention, air content, uniformity, band strength, minimize water penetration, durability, elasticity, auto genius healing, compressive strength, and Freeze-Thaw Durability.





Workability (Plasticity)


Bond strength is also assessed by the lime mortar’s workability (plasticity): a complete link between lime mortar and brick is essential to develop a bond, and the ease with which lime mortar spreads is dictated by the lime mortar’s workability. Workability depends on the lime mortar’s water retention, water content, and inside friction (determined by combined properties, hydraulic strength of binder and mix up proportions). In this research, workability was assessed by defining the mix consistency and measuring the outward flow of the fresh lime mortar (initial flow), and these results were related to research parameters including water retention and bond strength.


Lime enhances the workability (plasticity) of mortar while affording a high degree of

cohesiveness it also spreads easily under the trowel. Lime mortars have the plasticity of not less than 200 Emley units when tested by the Emley technique in the part on Plasticity of Lime mortar in Test Methods ASTM C110. Vicat consistency of the mortar should be adapted to the permeation of 20 ± 5 mm prior to working the Emley experiment. If permeation results are over 25 mm, the consistency of the lime mortar can be increased by allowing the mortar to settle and decanting off the excess water or

by the use of a sucking pad such as the one used for water retention test in Test Methods ASTM C110. If the permeation is below 15 mm, water should be added to the lime mortar to increase the penetration. When water is added to the lime mortar, the mortar should be mixed for a minimum of 15 s prior to testing the permeation.


Water Retention


Lime mortars have the highest water retention, generating an improved bond as there is more contact between elements and lime mortar. Retention of water in lime mortar boosts carbonation in pure lime mortars and results in best conditions for early hydration of lime mortars – thus minimizing cracking and water penetration into hardened mortar joints. Also, lime mortars lose water through evaporation, however, in contact with absorbent bricks, they lose water through suction. The highest water retention

allows lime mortar to sustain moisture for appropriate curing and bonding and maintain plasticity so that bricks can be aligned and level without disturbing the bond. When used with low-absorption bricks, lime mortars of low water retention bleed moisture, creating a layer of water at the interface that causes the brick to float thus decreasing bond.


Air Content


Air content in lime mortar concerning its density. Air content is useful to predict the mechanical strength of lime mortars. Air-entrainment additives can be added to lime mortar to augment water retention and plasticity. The highest point of air permitted for air-entrained lime mortar is 12% when structural support is implemented into the building material or when Types S and M lime mortar is used, and 14% when structural reinforcement is not used and Types N and O lime mortar is used. Analysis has shown,

though, that high levels of air entrainment can considerably diminish bond strength. Copeland et al (1964) found that if mortar air content is augmented from 5% to 20%, a 79% decline in lime mortar bond strength results. Fishburn (1961) found that bond power declines by 50% when lime mortars with 10% to 20% air-entrainment are tested. The water-retentive property of Type S hydrated lime mortar allows for workable mortars at low to moderate air entrainment levels.


Uniformity


Lime mortar provides uniform operation characteristics in the subject. ASTM C270 provides suggested proportions for Type O, N, S and M lime mortars. This specification also requires that hydrated lime products meet ASTM C207 criteria, Portland cement meets ASTM C150, and both ASTM C207 and ASTM C150 specify chemical composition as well as physical product qualities. The chemistry of each lime mortar mix together is defined and contains a superior percentage of cement materials (> 95%). Since

chemistry is well defined, performance characteristics such as compressive strength and flexural bond strength are predictable at given proportion levels. Air content of cement-lime mortars is restricted to 12% for Type M and S mortars and 14% for Type N and O mortars. Tighter limits on-air content also help to minimize variation between blends. Pre-blended cement-lime mortars are also available in most markets at 65-75 lb. bags, bulk bags or silo systems.


Bond Strength


Lime mortars have been given high levels of flexural bond strength. High tensile bond strength is optimized by the following properties of lime mortars:


Tensile Bond Strength - This is the strength of the lime mortar that keeps the building material units together. High tensile bond strength is formed by the following mortar characteristics:


Lime provides maximum water retention that permits the highest early curing of the

cementitious materials.


High initial flow that allows flawless total coverage of masonry units.


The little air content of lime mortar enlarges the bond strength of buildings.


The extent of Bond - The extent of the bond is the proportion of brick to which the lime mortar adheres. The small air content and the fineness and stickiness of hydrated lime mortar particles enlarge the extent of the bond of lime mortar to brick. These factors allow lime mortars to penetrate intensely into the bricks and seal the bricks/lime mortar interface.


The durability of Bond – Durability lime mortar has been determined by their Elasticity,

Autogenous Healing, and proven performance. All masonry construction is a durable, small maintenance mechanism. The use of lime in mortars bestows on the durability of the system.


Elasticity – Many researchers have shown that high lime content mortars were sluggish

hardening and remained elastic or flexible. Lime mortar augmented the capability of the

gathering to accommodate stresses caused by building the movement and periodic changes without too much cracking.


Auto Genius Healing - When micro cracks grow in the lime mortar, hydrated lime mortar

responds with carbon dioxide in the atmosphere. This reaction produces limestone which helps to seal/shut the crack.


Proven Performance – For Centuries, all ancient buildings were constructed by lime mortar. Since the invention and development of Portland cement, lime mortar usability has declined. Prior to this, the lime mortar was used as the primary ingredient of all mortars. The durability of these buildings functions as a testimony to the everlasting durability of lime mortars.


Minimize Water Penetration


Many studies and research have shown that lime mortars can be used to diminish the potential for water penetration into masonry walls. Minimize water penetration in the building’s walls special trait of lime mortar. Low air content, fine particle size, high plasticity, and water retention contribute to the excellent extent of bonds for cement lime mortars. This eliminates easy migration paths for water penetration.


Freeze Thaw Durability


When water freezes due to external cold, water expands about 9 percent. As the water in moist concrete freezes, it makes pressure in the pores of the concrete. If the pressure exceeds the tensile strength of the concrete, the cavity will enlarge and rupture. The aggregate result of consecutive freeze thaw cycles and the problem of paste and aggregate can eventually cause development and cracking, scaling, and breakdown of the concrete.


A freeze thaw cycle will be adequate to generate failure in the lime mortar joint. Lime mortar can also take a long time to completely cure and therefore work needs to be functioned at a time of year where the weather conditions are good for the lime mortar setting flawlessly. Those conditions are not only exceeding freezing temperatures but also drier seasons. To defend the slow curing lime mortar from damp, a Siloxane can be added to the surface. With historic structures, this may be a controversial strategy as it could have a detrimental effect on the historic fabric.


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