A void is an empty space in lime mortar. The type,size, shape, arrangement and abundance of voids and pores are factorscontrolling many important properties. The volume air voids is depend onmix design, preparation and application methodologies of lime mortars.
To studythe texture of lime plaster, it is essential to know the profusion of varioustypes voids. Air voids present are formed during the mixing limemortar. Diffusion of vapourous lime mortar into air voids may cause free growthof needle-like crystals from inner walls of such voids as in thecrystallization in miarolytic cavities 31 and 32. Particle size and particle size distibutionin the lime mortar and the planarsurface on which the lime mortar applied are also caused heterogenetity of lime mortar. They may be studied underscanning electron microscope (SEM).
Thesize and shape of the voids can be used as indicators of type and origin ofvoids. The luster and texture of the interior of the voids may be used in therecognition of voids caused by accumulation of water and passageways for water.The properties on which distinctions may be made between the various types ofvoids.
Because these distinctions aremade on the appearance of a void on the surface of a slice, many large voidswill be classified as entrained voids when they are really entrapped voids(>1mm bubble like (FHWA-RD, 1997). A cross section that is larger than thedefined maximum for entrained voids (100µm – 1mm) must be a section of an entrappedair void or a water-formed void. A significant number of large cross sections indicate agreat number of large voids. SEM study is a valuable technique to analyzequantitative determination of the abundance of various types of voids. Airvoids are classified as entrained or entrapped. During recrystallization offine-grained minerals into coarse crystalline ones, the whole material tries toloose the excess of internal energy generated during the deformation when the crystal lattice defects occurs.
Duringsuch process the shape and size of grains change and the texture of thematerial changes. The intergranular boundaries of mineral grains are irregular.During recrystallization of gypsum and other sulphate minerals, intergranularboundaries are migrated or rotated (Nimmo, 2004).
Adjacent grains differs in density.The defect poorgypsum grain bulges into the deffect rich adjacent grain, and shape of the gypsum grain distorted. It resultsspontaneous growth of new grains.
