Gulf Construction Online - Improved workable concrete from Fosroc

Chemicals in Construction

SCC offers several benefits.

Improved workable concrete from Fosroc

01 September 2005

Admixtures have for a long while played a vital role in the production of quality concrete and mortars in all segments of the industry – be it readymix, precast or site-batch – for its ability to add value and contribute to the successful production of concrete for specialised applications.

Historically admixtures have been used from as early as 300BC, when animal fat, milk and blood where used as additives to increase the properties of pozzolanic cement.
Over the centuries there has been a sea change in the nature and use of these chemicals, with contemporary admixtures – considered an environmentally friendly construction solution – increasing the long-term durability of concrete.
The latest admixture contribution to the constantly changing needs and requirements of the construction industry is the new generation hyperplasticiser derived from polycarboxylate ether (PCE). This superior PCE technology is steadily establishing a strong reputation worldwide and is now being specified for major projects throughout the Middle East, says a spokesman for Fosroc.
Fosroc’s Structuro products – based on PCE technology – enable the production of self-compacting concrete (SCC), which flows silently, with minimal friction and can be placed within the most intricate formwork or heavily congested reinforcement areas without the aid of any vibration or compaction, allowing the formation of structures with no bleed or segregation, while still maintaining the proper air void distribution.
Unlike conventional concrete mixtures, which are difficult to place in highly congested reinforced structural sections, SCC offers an ideal solution based on the correct balance of admixtures, higher percentage of fines and sand, plus a dramatically lower amount of coarse aggregate.
SCC also prevents the abnormal retardation, which in the past was linked to high concentrations of admixtures traditionally used in difficult applications and intricate formwork, says the spokesman.
A comparative graphical representation (Figure 1) between traditional and SCC mix design indicates that SCC incorporates a higher percentage of fines in the mix resulting in ultra cohesive concrete in spite of very high flowability.
This technology packs a wide range of benefits including:
• Faster placement in adverse conditions;
• Non-segregated flow within the most congested reinforcement;
• Enhanced concrete surface;
• Eliminates the need for vibration;
• Reduces labour costs; and
• Environment friendly and hence reduces noise pollution.
These qualities transfer beneficial cost implications for concrete producers, users and ultimately the client as the use of SCC could translate to savings in time, equipment and labour.
SCC offers a variety of benefits for the contractor when compared to conventional concrete materials. In many areas of construction, SCC delivers not only improved ease and speed of placement and better final surface, but also guaranteed complete compaction and elimination of voids, he points out.
Over the past five years the use of SCC has increased in popularity throughout the Middle East as contractors increasingly acknowledge the fact that it meets the demands of difficult placing and working practices.
Throughout the Gulf, Structuro has provided the solution to a number of difficult design challenges on major prestige projects including:

Shangri-La Hotel, Dubai
One of the main challenges of the project was a design requirement to allow the pumping of concrete to a height of 184 m. Consequently it necessitated special admixtures to provide high workability and fluidity. In addition, the dense reinforcement provided little scope for concrete vibration, which made it absolutely necessary that the concrete flow under its own weight, explains the spokesman.
The self-compacting concrete admixtures, consisting of Structuro 335 and Structuro 480, met the specifications and about 780 cu m of SCC was pumped to a height of 184 m on transfer beams that support the entire steel structure on the roof.
'This was a breakthrough in self-compacting concrete as it represents the highest SCC application in the Middle East, Near East and Europe,' says the spokesman.
Other successful applications of polycarboxylate ether technology in the UAE include the Beirut Tunnel in Dubai, Dubai Islamic Bank Tower at Dubai Marina, water tanks for residential and commercial complexes in Sharjah, the Third Bridge Crossing in Abu Dhabi and various other projects.

Water Treatment & Reclamation
Sulaibiya water treatment and reclamation project – the first BOT project executed in Kuwait – consists of over 30 tanks with multiple pipe penetrations through each tank. One of the major challenges on the project was that the outlet boxes were heavily reinforced and access was limited making it very difficult to vibrate conventional concrete in such a restricted area. Yet it was critical that the pipe surrounds have good quality concrete to prevent any leakage around the openings, he adds.
The consultant and contractor concluded that SCC was the most viable solution under the difficult working conditions. To date, approximately 600 cu m of concrete have been poured successfully on this project, he says.

Az Zour Gas Turbine
Explaining the challenges he says: 'Precast concrete piles were specified for part of this project. The concrete mix specifications contained OPC and GGBFS 40 per cent and 60 per cent respectively, in addition to the use of calcium nitrite at the rate of 15 litres per cu m.
'The design parameters and difficulties of maintaining the workability of the concrete for 30 minutes due to the inclusion of calcium nitrate additives required that hyperplasticiser was included in the concrete mixture and Structuro 335 was, once again, the product that offered the solution,' he adds.