Cement, Energy and Environment

Brick-mortar bond strength There should be good bond between the mortar and the brick for the masonry to perform sa sfactorily. Bond strength becomes significantly important when the masonry has to resist tensile and shear stresses. Large number of parameters pertaining to bricks/blocks, mortars and construc on prac ces influence the masonry bond strength. Surface characteris cs of the masonry unit (pore size distribu on, porosity, etc.), moisture content of the unit at the me of construc on, absorp on characteris cs of the unit and mortar composi on are some of the important characteris cs influencing brick-mortar bond development. Brick-mortar bond strength of the Masonry Prism was tested using Bond – Wrench test as per ASTM C1072. Flexure bond strength of masonry prisms using local burnt clay bricks and the 1:6 cement mortar with Manufactured Sand and river sand was determined. Six prisms were tested in each category to get the mean value of flexure bond strength. The flexure bond strength of masonry using 1:6 cement mortar (with 85% flow) was 0.06 MPa and 0.15 MPa for river sand and Manufactured Sand mortars respec vely. The flexure bond strength of masonry prism improved by 150% when Manufactured Sand was used instead of river sand in the 1:6 cement mortar. Compressive strength of masonry Compressive strength of masonry was examined by tes ng five brick high stack bonded masonry prisms. Prisms (size: 105 x 225 x 445 mm, having height to width ra o of 4.23) were prepared using burnt clay bricks having compressive strength of 10.1 MPa (mean value) and using 1:6 cement mortar with river sand and Manufactured Sand. Compressive strength of the masonry prisms was 3.35 MPa and 4.38 MPa for mortar with river sand and Manufactured Sand respec vely. Nearly 30% increase in masonry strength was observed in mortar made with Manufactured Sand . Concluding Remarks The mining of sand from riverbeds is being regulated by the statutory authori es, as indiscriminate mining is causing damage to the environment. This has resulted in shortage of sand hampering the construc on ac vity. Realizing the severity of the problem, the Governments of various States have allowed the use of Manufactured Sand (not Crusher dust), as an alterna ve to River Sand a er establishing the performance of Concrete and Mortar containing Manufactured Sandas fine aggregates. A case study ini ated by Karnataka Government at IISc reveals that the characteris cs of mortars and concrete using Manufactured Sand as fine aggregate are superior when compared to mortars and concretes using natural river sand as fine aggregate. Manufactured Sand falling within the grading Zone II as specified by IS 383 manufactured from the hard rock is suitable as fine aggregate in concrete and masonry mortars. Also, IS- 2116 and IS 383 codes permit the use of crushed 6 Stack bonded masonry prism under compression test Fig (a) Typical failure pa ern, Fig (b) Prism with strain gauge