Grand Housing Development Program Volume III - Gtz

CONSTRUCTION GUIDELINE STEP BY STEPConcrete workThe required strength of the concrete should be givenin the structural drawings. The mixing rate for the requiredstrength varies according to different conditions.There is no general mixing rate. The rate and thewater-cement ratio depends on:• weather conditions (sunny and hot - rainy andcold),• dry aggregates / wet aggregates• sizes of aggregates,• condition of sand (washed, silty, dry, etc.),• type of cement.It is recommended to prepare test cubes with differentmixing rates which have to be tested in an official laboratoryin order to find out the right mixing rate underlocal conditions.Footing columns1.5 m , the aggregates will be separated duringthe filling!• Is the formwork for the footing columns well installed(height and width)?• The formwork should not be higher than 20 cm ofthe finished concrete level!!!!• Are enough supports for the formwork installed?• Is the bottom (footing) clean and free fromorganical material?• Are all reinforcement bars installed accordingly tothe structural drawings?• Are the right bar diameters installed?• Are the spacers in between the reinforcement andthe formwork installed?• Have the spacers the right dimensions (distancebetween bars and formwork min.= 2.5 cm)?Before starting the concrete work for the footing columns,a written approval from the resident engineermust be given.(CONTINUED)The construction of the footing columns should bechecked according to the following list:B ACKFILL OF EXCAVATED AREA AROUNDFOOTINGCOLUMNS• Spacers should not be higher than the upper levelof the concrete!!!!• Is the future height of the concrete (filling height)levelled and visibly marked at the formwork?• If the filling height of the concrete is more thanBefore starting the back fill work the resident engineermust approve the materials (selected material) for theback fill work.Lean concrete and grade beams24Addis AbabaCity Government