Sab 2112 - L8 Concrete On Site

SITE CONCRETE

Concrete on Site Production of site concrete Compaction and curing Formwork Construction joint Hot weather concreting

Production of Site Concrete Access The need to provide access for delivery materials may impose limitations on site The most frequent deliveries will be of aggregates and cement OR ready-mixed concrete Site road must capable of withstanding the traffic

Storage Materials must be properly stored Storage must be adequate for all materials Cement must be kept dry Aggregates should be stored accordingly to avoid mixing with different sizes

Batching and Mixing Batching of cement and aggregates should be by weight Batching by volume may be suitable for small batches If sand is wet and batching is by volume, allowance must be made for ‘bulking’ (an increase in volume)

Batching Plant

Readymix Concrete

Need to consider Moisture content of aggregate Type of concrete mixer Mixing sequence and time Workability Ready-mixed concrete

Placing of Concrete Crane and skip Pumping Wheelbarrow, dumper trucks, railcars

Compaction Compaction is to eliminate air from concrete, reduce voids Compaction – internal (poker) and external Compaction is important to produce the required strength and durability of concrete

Curing Is the means of protecting moisture inside the concrete from evaporating to the atmosphere More critical for concrete with pozzolanic material

Curing methods Wet hessian/sacks/gunny Spray with water/chemical Cover with plastic sheet (opaque) Ponding with water (for slab)

Do Proper Curing Will You……

Effect of Curing

Formwork The shape of concrete member will be in accordance with the formwork Formwork must be stiffed so that the shape of the finished product will not be altered Formwork must be impermeable Formwork materials – timber, steel, plastic, others

Construction Joints Generally it is not possible to place concrete continuously, need to provide construction joints Construction joints should be located and formed with care, and their number kept to a minimum Is used to eliminate cracking problem due to expansion and shrinkage Movement of concrete can be due to moisture or temperature difference Joint

Hot Weather Concreting Concrete sets quicker in hot climate Need to use retarding admixture Slump loss is easily to occur Curing is very important Plastic concrete should be protected from sun and wind

Gracias