IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 14, Issue 2 Ver. VI (Mar. - Apr. 2017), PP 65-71 www.iosrjournals.org DOI: 10.9790/1684-1402066571 www.iosrjournals.org 65 | Page Effect of Some Additiveson Mechanical and Physical Properties of Cob Building in Iraq Manar Nazar Ahmed 1 , Payman Sahbah Ahmed 2 , Samal Osman Saied 3 1,3 Architectural Engineering Department, Koya University, Koysinjaq, Kurdistan, Iraq 2 Manufacturing Engineering Department, Koya University, Koysinjaq, Kurdistan, Iraq Abstract:Construction materials needs to be low energy consuming and mud construction system is less energy consuming and very successful in different weather conditions. Cob is an old earth building method passed down through the millennia, Cob is a sustainable earth building material with mud soil, coarse sand, straw and water are thoroughly combined and beaten together. This research aims to study the effect of some additives on physical properties (thermal conductivity and water content %) and mechanical property (compression strength) of Cob. These additives are: polymethyl methacrylate (PMMA) grains, hooked end steel fibers (HESF), wood as sawdust (SDW) and goat hair fibers (GHF), with 2 and 4 % by weight as the percentages of additives. Results shows that (PMMA) improves the insulation of Cob to maximum values compared to other additives in both 2 and 4 % followed by (SDW) and (GHF) respectively. All additive materials improve the compressive strength of Cob but with different extents depending on the water content. (GHF) is the best material to improve the compressive strength of Cob followed by (HESF) and (PMMA) respectively while adding (SDW) will lead to reverse effect i.e. decreasing the compressive strength. Keywords:Cob, thermal conductivity, compressive strength, goat hair, hooked end steel fiber, PMMA. I. Introduction Architecture requires use of diverse construction materials that require a special constructionmethods. But most of these construction methods are energy concentrated. All the traditional resources are consuming which has made it compulsoryto choose materials and construction systemswhich require less energy for its performance. Mud construction system is less energy consuming and verysuccessful in different weather conditions. Earth is one of man's oldest building materials and most oldcivilizations used it in some form. It was easily available, cheap, and strong and needed only simple technology [1] in addition to its excellent sustainable characteristics [2].Some of the method utilized for earth building construction around the world incorporate utilizing mud bricks dried by the sun (earth brick), wet soil placed between removable form boards (rammed earth), wet mud soil mixed with straw placed by hand to form walls (Cob), or clay reinforced with woven or liadwood (wattle and daub) [3]. Cob is an old English word that means lump or rounded mass [4] or the English name for mudwall [2]. Cob is an old earth building method passed down through the century and known by many names in many countries.Basically, Cob is building with mud. Clay soil, coarse sand, straw and water are thoroughly combined and beaten together. This stiff mud is thenbuilt up into walls while still wet on a foundation of stone and lean of concrete.The mixture is applied in feeds, each of which is "stitched" into the onebelow while both are still flexible. As the bottom of thewall becomes strong and dry, more Cob is added on top until the desired height is reached, with doors, windows, plumbing, electrical conduits, wooden anchors for cabinets,etc., being built in the same time. The roofs made from beam of wood covered with tibial and Cob as shown in figure 1. Walls then covered with mortar of cement as a final step after Cob is dried. The result is a very hard, strong, homogenous earth wall, strengthen by a continuous interwoven matrix of high tensile-strength straw fibers suitable for rural areas in Iraq. Fig. 1.Section by Cob for rural areas in Iraq (left)construction of wall (right)- Drawn by authors.