SUSTAINABLE SOLUTIONS IN CONCRETE INDUSTRY GSAS Sponsored Seminar / Workshop MEETING TODAY’S DEMANDS BY ADOPTING THE LOW CARBON CONCRETE REVOLUTION Christopher Stanley, Technical Director, Unibeton Qatar National Convention Centre, Doha – Qatar 24th May 2014
What is Sustainability? • Producing great structures that last • Using least possible energy both during construction and remaining service life. Embedded CO2 and operational CO2 need to be considered • Eliminating future maintenance costs. 120 year design life can now be extended to 400 years. • Leaving a better world to our children • Better durability: against chlorides, sulphates, ASR, acid attack • Better colour – high light reflectance
What is Low Carbon concrete? • Low Carbon Concrete is a GREEN concrete. That does not mean concrete that has not yet hardened, or is coloured with green pigment, but in the context of this presentation green concrete is taken to mean environmentally friendly concrete. • This means concrete that uses less energy in its production & produces less carbon dioxide than normal traditional concrete.
Where does the Carbon Dioxide come from inconcrete? • The main ingredient in cement is Limestone (Calcium Carbonate CaCO3 ) • During manufacture the ingredients are heated to about 1200oC • During this process the Carbon Dioxide is driven off : CaCO3 = CaO + CO2 • 1kg of cement releases 700gms -1kg of Carbon Dioxide into the atmosphere during its manufacture
Low Carbon Green concrete • Most of CO2 in concrete is from the cement manufacturing process (1 kg of cement produces about 1 kg of CO2 or 5 m3 of CO2) • Low Carbon Green concrete makes more effective use of cement giving a reduced carbon footprint and therefore protects the environment. • Low carbon green concrete = effective use of cement means better not lower quality
A typical 40N concrete mix generates 100 balloons of CO2 per cubic metre of concrete
If some of the cement in the mix was replaced with GGBFS GGBFS (say 70%) = 294 kg x 0.109 = 32 kg of CO2/m3 126 kg of cement x 0.797 = 100.42 kg CO2/m3 = 32 kg CO2/m3 + 100.42 kg CO2/m3 = 132.42 kg CO2/m3 REPRESENTING A REDUCTION OF 201.58 kg CO2/m3
A 25% replacement of Portland Cement with PFA 25% PFA = 105 kg x 0.06 = 6.3 kg of CO2/m3 + 315 kg of cement x 0.797 = 251.06 kg CO2/m3 Total of 257.66 kg, or a saving of 76.35 kg of CO2 replacing 25% of the cement with PFA
Low Carbon Green concrete • Cement production accounts for 6% of all CO2 emission which is claimed to be one of the factors influencing global warming. • In 2013 Qatar was the highest cement consumer per capita in the world. • 1 Qatar 3.9 tonnes/year/capita 2 UAE 2.6 tonnes/year/capita 3 Kuwait 2.2 tonnes/year/capita 8 Saudi Arabia 1.4 tonnes/year/capita 40 Oman below 0.6 tonnes/year/capita
LOW CARBON GREEN CONCRETE OPTIONS • Highly optimized mix design • Self-compacting concrete • Ground granulated blastfurnace slag • Pulverised fly ash. (Pfa) • Portland limestone cement • Rice husk ash cement • Rice husk cement • Cement free concrete • Concrete wood • Low cost construction
Optimized Concrete Means Value Engineering • Better Performance • Enhanced cohesion workability, finishability and consistency • Reduced shrinkage / creep. Lower compressive strength SD • Durability - Increased service life of concrete • Greater Value • Minimizes amount of steel needed • Higher MOE can allow reduced section thickness weight • Optimizes use of available materials • Greener • LEED Contributes to Certification points • Reduced carbon footprint • Affordable “green” alternative
MIX OPTIMIZATION The basis for optimization is that the small particles can fill the space between the large ones to minimize the void content which creates maximum stability.
Aggregate proportions affect the properties of concrete • The slump of the concrete and its flow are a function of the angle of repose, shape & the quantity of the predominant size of the aggregate in the mix. • Use of more fine aggregate, because of the smaller angle of repose, gives higher slump & flow. • But the optimum proportions of coarse & fine aggregate are critical to the properties of both fresh & hardened concrete.
“Particle-Packing Optimization” to meet requirements of plastic and hardened properties”
Typical spread of an optimized mix – note theaggregate distribution & that it does not bleed
Heat of hydration • The heat of hydration of optimized modified concrete is significantly lower than traditional concrete • This results in a lower temperature rise in large concrete pours which is a distinct advantage. • The peak temperature rise can be reduced by up to about 14oC.
A typical 40N optmized mix produces only 27 balloons of CO2 per cubic metre of concrete
Low Carbon Optimized Green concrete gives value engineering • Better performance • Enhanced workability,finishability & consistency • Reduced creep & shrinkage • Increased service life • Greater value • Minimises amount of reinforcement • Higher Modulus of Elasticity – reduced thickness • Ease of compaction – less labour • Greener • Contribution towards LEED Certification points • Upto two ESTIDAMA points in UAE • Reduced Carbon Footprint • Affordable Green construction
VERY GREEN CONCRETE • Unibeton is now developing a technology to make very green concrete, sometimes even without Portland Cement, using a special process. This concrete will produce only about 7 balloons of CO2 per cubic metre. The concrete sets and hardens like Ordinary Portland Cement. It has a one day strength of about 22MPa and 28day strengths of 60 – 75 Mpa can be achieved.
No-cement concrete • By 2050 global use of cement likely to be 5,000Mt (steel will be 8,000Mt). • No-cement concrete could be 1/3rd so 1,666Mt or 4,700Mm3 of cement-free concrete. • Highly likely that PFA and other byproduct pozzolans will increasingly make “greener” concrete and reduce embedded CO.
Our solution • Use a cement replacement (binder) based on the activation of ground granulated blast furnace slag (GGBS) and pulverised fuel ash (PFA) byproducts. • Both are widely available and relatively inexpensive. • GGBS and PFA must be activated to produce a binder. There are recently invented new types of activators. • Resulting binder used in much the same way as Portland Cement without the carbon legacy.
No Cement ConcreteThe technical advantages • Sets chemically with very low heat of hydration • Vast areas poured without joints- increased productivity • No early-age thermal cracking – take out reinforcement • 30 MPa in 7 days, >50 MPa at 90 days, and >70MPa at 365 days • Greater dimensional stability – low shrinkage and creep • Resistant to chloride, sulphates and acids • Maintenance-free. Much extended service life • Complies with performance based standards such as ASTM C1157 Low Heat Concrete category
Green Pre-stressed Concrete Advantages • Cost similar to most concrete used in GCC containing Slag or PFA • Green alternative only 7% of carbon footprint of traditional OPC concrete • Significant Carbon Credits due to reduction of CO2 emissions • Track record of use in pre-tensioned pre-stressed concrete in USA
Green Pre-stressed Concrete Advantages • Green cement free concrete can currently be produced in strengths ranging from 20MPa to over 75MPa • Current pre-stressed production normally calls for a concrete strength of 24MPa at the time the tendons are released and with a final strength of in excess of 35MPa. • The early strength gain can be adjusted to suit the production process but is normally in the region of 24hr-48hr before tendon release.