Construction World June 2016

RES

Pumping technique can also contribute to exacerbating the situation and the hopper should always be completely full to ensure that air is not sucked into the pump and that a constant pumping pressure can be maintained. It is also important that the integrity of the equipment being used is sound as a leaking pump or pipes will introduce air and affect the pumping pressure. “It is vital to look at the concrete pumping application and deter- mine the most appropriate admixture that will fulfil the requirement. This will also ensure the integrity of the final concrete product,” he says. Use of chemical admixtures means that concrete can now be pumped under a broad range of conditions, and this includes farther, higher and faster than previously possible. Admixtures also enhance the physical properties of the hardened concrete. Correia says that adjusting or changing the admixture selection can facilitate the required properties for pumping. “It is also important to understand that one superplasticiser will not suit every concrete application or type of cement as each is specifically designed to achieve a maximum performance with a certain type of cement chemistry,” Correia says. He again points to the need for construction companies to work with reputable material and chemical admixture suppliers to ensure that a fit-for-purpose concrete mix design is achieved that will fulfil the specific project requirements. Examples throughout the world A good example of a project where Chryso® Fill Free® technology is being used is the World One residential buildings in Mumbai India. At a height of 442 metres, these will be the tallest residential buildings in the world and the high strength concrete superstructure, with 100 MPa walls, uses the innovative Fill Free® admixture technology. Correia says the extreme pumpability offered by the product is ideal for such a super tall structure. Local examples of projects that have used Chryso® admixtures to achieve concrete pumping success are the Impala Platinum No 16 shaft and the Michelangelo Towers. At the time of construction, No 16 Shaft was the tallest mining headgear in the world with its structure reaching 132 metres high with 109 metres above the ground. With wall thicknesses between 550 mm and 950 mm, the shaft structure has a width of 20 metres and a breadth of 21 metres. Construction was achieved using slip forming method- ology and Chryso® Fluid Optima 100 was used to give the mix extended workability without affecting the setting time. Correia says that this enabled the contractor to speed up the pace of construction and resulted in cost savings on the project. Chryso® Omega 140 and Chryso® Optima 100 was used during the construction of the Michelangelo Towers. This admixture was selected to reduce pump pressure which facilitated pumping of the concrete to the top of the structure at 143 metres.

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It is vital to look at the concrete pumping application and determine the most appropriate admixture that will fulfil the requirement.

CONSTRUCTION WORLD JUNE 2016