The effect of egg albumen on the physical AND MECHANICAL PROPERTIES of lime mortar
1Tiong Ling Ling, 2Md Azree Othuman Mydin
1,2School of Housing, Building and Planning, Universiti Sains Malaysia 11800, Penang, Malaysia
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ABSTRACT
Most historic and traditional mortars were made with lime. Due to their nature and function, lime mortars erode and need to be replaced. However, lime mortars cannot be replace by the cement-based mortars due to incompatible with the construction materials of the original masonries, cement-based mortar doesn’t respect the features of the originally applied materials and traditional technology then will causing structural and aesthetic damage. The best solution is still conserving those heritage buildings by using the lime as it was proved that lime is mechanically compatible [1][2][3] with the old bricks and stones which are relatively weak and porous. There is scare of literary evidence to study the effect of organic materials on mechanical properties of lime mortar. This paper aims to investigate the effect of egg albumen on the mechanical and physical properties of lime mortar. A total of 5 mortar mixtures and 1 control mixture were designed having a constant lime/sand/water ration of 1: 2: 0.035. The control mixture include only lime putty as the binder while the remaining mixtures were mixed with different percentage of egg albumen range from 2% to 10%. An experimental work was carried out to investigate the axial compressive and flexural strength of lime mortar with different percentages of egg albumen and examine the water absorption. The results indicate that the strength of lime mortar increases directly proportional to the percentage of egg albumen added into the lime mortar until it reached 6% of the egg albumen. It dropped when the 8% and 10% of the egg albumen added into the lime mortar.
Keywords: Lime mortar; Lime putty; Egg Albumen; Workability; Compression test; Flexural Test; Water Absorption
1. INTRODUCTION
Currently, lime has become one of the principal materials used in the conservation and restoration of historic buildings. It is one of the most suitable and long lasting building materials used in mortars, plasters, and paints for centuries. This is because lime has many attributes that make it suited for use in masonry restoration. These mortars have a high mechanical resistance, increased waterproof protection, and antifungal properties. Unlike today’s framed structures with masonry veneers, traditional masonry structures were just that solid masonry [1]. The thickness of the walls kept moisture out of the living space and provided strength. Inevitably, the thickness of the walls also guaranteed they would constantly contain. This all worked very well with lime mortars, plasters, and paints (lime wash) because lime is able to absorb large amounts of water, and due to its porosity, very easily release the moisture back into the atmosphere. Substitution of modern materials for historic lime based materials can lock moisture into walls causing a myriad of problems including failure of masonry units, interior water damage and structural failure of interior wythes of the wall [2].
Traditional materials like lime mortar, natural cement, Roman mortar, etc are highly recommended because modern research and history have confirmed that some of them exhibit good compatibility, appropriate strength with ancient buildings, and are more effective than modern materials. The major advantage of lime is that when used in mortars, it has higher bond strength than unmodified non-lime mortars. Lime has a much smaller particle size than other common mortar binders (e.g. 1/500th the particle size of Portland cement) consequently lime more effectively fills and bonds the pours of your brick or stone. Additionally, because lime creates creamier mortars, there is no need to introduce air entraining agents to the mix. Air entrainment creates bubbles and lessens the surface area contact between the mortar and the brick and stone. The use of traditional lime materials exist some challenges. Lime cures differently and by different mechanisms than modern materials. The curing process can also be more affected by adverse weather conditions. In fact, masons and craftspeople well versed in modern materials often have problems installing lime materials. Figure 1 show the simplified lime cycle and hydraulic set [3].
This simple lime cycle is based on pure limestones producing ‘air limes’ (also termed ‘non-hydraulic’ limes). Lime production from limestones containing reactive materials (siliceous or argillaceous limestones), proceeds via a more complex cycle to produce ‘natural hydraulic limes’ (NHLs). Hydraulic limes set not only by carbonation, but via hydration reactions occurring between the silicate and aluminate components with water and calcium hydroxide. This ‘chemical’ setting mechanism enables the use of hydraulic limes in wet conditions, where air limes would fail to set. Natural hydraulic limes are typically stronger and less vapour and moisture permeable than air limes. The production of lime from limestone via this cycle is a well-established and ancient technology, probably brought to Britain by the Romans. Although the lime production process has remained largely unchanged for thousands of years, on site additions and modifications to the raw material have evolved over time. Builders have experimented with different materials for different applications, often making the lime more workable, quicker setting or achieve water resistant properties. Traditional additives used to achieve these qualities included animal fats and blood, milk and volcanic ash
Figure 1: Simplified lime cycle and hydraulic set
In conservation repair work, it is imperative that an understanding of the building or structure is gained before specifying and undertaking any works. This is particularly important for lime-based works. An original mortar might have inherent defects. Buildings and their surrounding environment may change over time: for example, a residential building may now be a roofless ruin. Repair mortars can, and sometimes should, be designed to perform in a different way from original mortars to meet new performance requirements.
Lime mortar was not commonly used until it was utilized by the Greeks and this knowledge of mixing mortar was then took by the Romans around the 1st millennium BC. Another most important reference of lime mortar comes from Vitryvius, a Roman architect, the writer of Opus Incertum, which provide a guide for building works and for mixing lime mortar around 25 BC. Even though the Romans did not fully understand the properties and technology of how hydraulic lime works, they did notice the need of such mortar to include pozzolan such as crushed ceramic, volcanic ash and crushed brick within mortar mix to solve the problems. Romans were great innovators, they constantly looking to improve and experimented by modifying lime mortar mixes with controlled additions of naturally occurring deposits. There is only little known about the use of lime mortar during the fall of the Roman Empire and the medieval period, the traditions continued to have been implemented but on a smaller scale than before. In addition, the use of stone structures and lime as a binder rise rapidly in the construction of numerous castles and churches that built by William the Conqueror within England in 1066.
The most significant evolution in the use of pozzolans in lime mortars can be traced back into 18th century. It was found out that burning limestone that containing clay would produce hydraulic product. John Smeaton was the first person who developed hydraulic lime product in 1756 and an Italian pozzolanic earth from Civita Vecchia also added in order to improve the strength. This mixture was used to construct Eddystone Lighthouse. In 1796, Roman cement or natural cement was invented by James Parker. Natural cement mortar was used in construction where masonry was subjected to moisture and high levels of strength were needed due to it had higher clay contents than hydraulic lime products that allow for better strength development. This mixture was widely used until the late of 1800’s. In 1824, Portland cement that consisted of a blend of limestone, clay and other minerals in carefully controlled proportions which were calcined and ground into fine particles was invented by Joseph Aspdin. Portland cement replaced natural cements in mortars due to its consistency and higher strength. Mix design of different amounts of lime and Portland cement were developed because the addition of Portland cement to lime mortars will help to improve the speed of the construction process for masonry building due to its faster strength development. Due to the newly invented Portland cement, lime mortar was slowly phasing out from construction industry and replaced by Portland cement.
In the late 19th century, the importance of preserving the heritage building and historic environment was realized. It requires full understanding of both structural and architectural qualities and the construction materials and methods used in order to successful repair of ancient buildings. However, the knowledge of lime and its inherent qualities, the mainly materials that mostly used in old buildings was lost. As a result, Portland cement based materials was largely applied to the existing lime mortar masonry for the repair and restoration work that carried out in the 20th century. In 1977, Building Research Establishment found that all the masonry buildings that repaired or restored by using the Portland cement tend to deteriorate faster than those without undergone any major repairing and renovation works. The old masonry buildings that repaired with Portland cement or plaster showed the sign of destructive failure in less than ten years. This is because hard cement mortar is physically and mechanically incompatible with old masonry buildings that built by lime products which are relatively weak and porous. It is important to identify the precise nature and means of production of historic mortars and lime based materials.
In this study, the organic material which is egg albumen will be added into the lime mortar in order to modify the properties of lime mortar. No sound scientific explanation for the use of egg albumen in lime mortar is available. Nevertheless, egg albumen, due to its protein concentration, is a powerful binding agent since proteins are slightly elastic in nature, as well as tending to bind together. According to S. Chandra and J. Aavik (1987), egg albumen or also can be protein work as air entraining agents in cement mortar. Such additive was used to improve the properties of a mortar before or after set such as workability and durability. Being organic, this type of admixture would be expected to disappear from the mortar relatively rapidly, leaving no detectable traces.
2. LITERATURE REVIEW
2.1 The reason of using lime in mortar/building
Lime was used as universal binding material in mortars and plastering works for most of the historical masonry building. Lime has many advantages and one of the reasons is lime allows buildings to breathe [4]. They are vapour permeable thus reduces the risk of trapped moisture and consequent damage to the building fabric. In addition, lime provides a comfortable environment due to its porous and open textured materials such as lime plaster, it can help to stabilize the internal humidity of a building by absorbing and releasing moisture. Therefore reduces the surface condensation and mould growth. The use of lime has ecological benefits such as less embodied energy than cement; free lime absorbs carbon dioxide in the setting process of carbonation; it is possible to produce lime on a small scale; the gentle binding properties of lime enable full re-use of other materials and small quantities of lime can protect otherwise vulnerable, very low energy materials such as earth construction and straw bales. moreover, lime able to bind gently with the early adhesion because the fine particle size of lime, far smaller than cement, is linked to the root meaning of the word lime, which is “sticky material”. Due to the fine particle size, lime mixes penetrate minute voids in the background more deeply than other materials. They bind gently and the stickiness gives good adhesion to other surfaces. Besides, the characteristics of lime mortars with high free lime content are porous and permeable that allows lime mortars to protect adjacent materials by handling moisture movements through the building fabric and protecting them from harmful salts. The most important characteristic of the lime as to be used in building is self healing. The nature of ground conditions and the elements are such that all buildings are subject to varying degrees of movement over time. When buildings made with lime are subject to small movements they are more likely to develop many fine cracks than the individual large cracks which occur in stiffer cement-bound buildings. Water penetration can dissolve the “free” lime and transport it. As the water evaporates this lime is deposited and begins to heal the cracks. This process is called autogenous or self-healing [5].
2.2 Properties of fresh mortar
According to Mortar Industry Association, it stated that the role of fresh mortar during construction were a very important and complex one, where the mortar must spread easily and remain workable longs enough to enable the accurate laying to line and level of the masonry units. In addition, it also must retain water so that it does not dry out and stiffen too fast, especially when using the absorbent masonry units. As a result, it must then harden in a reasonable time to prevent it deforming or squeezing out.
2.3 Workability of fresh lime mortar