The effect of tectosilicates micronized additives on physical and mechanical properties improvements of Cob (Kahgel) plaster

Abstract

Kahgel (Cob) is one of the oldest traditional mortars in Iran. Kahgel plaster consists of high clay content, dried mud and a portion of straw fibers to defend the mortar against shrinkage cracks. The ancient waterproof covering is very efficient at protecting the building dry during the heavy rain showers, but low durability and the need for renewal of plaster due to erosion of rainfall suggest that Kahgel plaster is weak and unstable. So, it is very essential and necessary in finding appropriate scientific methods to enhance the durability and lifespan of Kahgel plaster. Studies on the stabilization and improvement of Kahgel plaster properties indicated that using some special tectosilicatesadditives can be improved significantly the physical and mechanical properties of earth and earthen materials such as Kahgel plaster. The effect of different micronized tectosilicatesadditives used to build the different samples of Kahgel plaster on physical and mechanical properties to enhance the durability of Kahgel plaster showed that Microsilica at 6% (by weight of Khahgel), reduced hydraulic conductivity of the Kahgel plaster at 33% level and micronizedZeolite at 3% (by weight of Khahgel), is increased by 85%. In addition Microsilica and micronizedZeolite at 3% (by weight of Khahgel), increased compression strength of the Kahgel plaster at 73% and 36%, respectively. In addition micronized Kaolin and Bentonite, increased uniaxial compression strength of the Kahgel plaster at 39 % and 33 %, respectively. In addition evaluation of water erosion of the samples during rainfall by rainfall simulator showed that use of Microsilica, Feldspar, Zeolite and Kaolin 3% (by weight of Khahgel), the minimum sample’s total dry material loss of the Kahgel plaster reduced to 10/5% and the maximum decrease to 37/7% and increase durability of the Kahgel plaster against water erosion. Experimental results indicated that in addition to the type and percentage of additives, particle size plays an important role on the physical and mechanical properties of Kahgel plaster.

Keywords

• earthen architecture kahgel
• micronized additives
• tectosilicates
• conservation