BTS/CONCRETE | TECHNICAL


CONCLUSIONS Geopolymer concretes provide a great alternative to high replacement mixes by providing much higher CO2


savings and good performance. Cost, however,


can be prohibitive and EFC is currently 30%-40% more expensive, albeit this will reduce with more UK usage. Availability has been London-centric. Capital Concrete


had one plant, now two with one more to come. However, with Wagners now making the activator in the UK it is possible to tankerise the activator and modify an existing plant for use, depending on volume required. All staff need to be briefed on use, and designers and


clients need confidence that requirements can be met and testing will do this. Collaboration across the project is essential to reduce carbon and this requires a culture of trust and cooperation, and the speakers would like to extend a big thanks to all parties involved. Murphy and National Grid have also separately trialled


Cemfree concrete, which is an alternative geopolymer concrete. It comes in bagged form and can be used anywhere in the UK. From November 2020 to November 2022, Murphy


were part of the LOCOWAG (Low Carbon Concrete in Aggressive Ground) Group. As part of this Murphy Ground Engineering (MGE) conducted two trials: at HP11 Austry – Barton Gas Pipe Diversion for Cadent; and, at Newman Street, Westminster. Both projects used Cemfree in piles. Cemfree met the design requirements for these


temporary works applications. Trials were successful for the proposed use but showed less strength gain than EFC with C28/35 being reached at 56 days, and durability test results are awaited. MGE won a sustainability award at the Ground Engineering Awards for this work. Based on this testing, Cemfree can certainly be recommended for temporary works applications but more test results would be needed to support a permanent use. NG worked at its Deeside Centre for Innovation with


Cemfree, BRE, Hanson, and Centrum Piling over a similar period. It arrived at very similar conclusions on strength and durability.


FINALLY Everyone has a part to play in carbon reduction; ● Clients need to decide how much worth to place in lower carbon solutions


● Designers/Clients need to allow use of alternative materials through performance based, rather than prescriptive, specifications


● Designers need to take a pro-active approach to using test results and remember that EC2 allows testing


● Contractors need to push benefits and adopt where they can


● Everyone should raise awareness, work together, set targets, plan, and share data


Information sharing is important. HMJV and NG are thankful for historic data from both Aecom Australia and Byrne Brothers, and our experiences from LPT-2 will be made available to others.


Question: It was stated the properties of the product are improved as well as carbon. Would the market pick it up even if it didn’t bring any carbon saving? EFC was developed as a reaction to Australian carbon tax but the tax was removed and testing continued, primarily


due to the increased durability being experienced. Both CO2 benefits and performance are particularly evident in the higher grades of concrete in aggressive environments.


Christoph Eberle (Mott MacDonald): i) Is there a practical upper limit to strength? C25-C65 in accordance with standard but can get up to 90MPa-95MPa cylinder strength.


ii) Is the correlation between compressive strength and tensile strength the same as for normal cement-based concrete? The higher grade you go the closer this relationship is to what you’d expect. However, in general, you get more flexural strength and split tensile strength from a given compressive strength, primarily due to a lack of bleed in the mix.


Dr Clive Chin-Kang Shen (Arcadis): Is this technology sprayable, or solely cast? It is sprayable and we [Wagners?] have undertaken spraying trials both with and without fibres at the University of Queensland and numerous applications such as swimming pools and the product is low bleed and cohesive. What we haven’t fully developed yet is acceleration at the nozzle and we are studying that now.


Jude D’Souza (Murphy): Any safety benefits or disbenefits as compared to OPC? Fresh properties are very similar although pH is higher. The same safety controls are needed as more conventional, standard, concrete, so as to ensure wash off.


Andrew Chappell: Does the UK produce enough GGBS and PFA to meet the demands of such geopolymer mixes being used widely? More an issue of logistics than availability. Effectively, just a switch from cement import to GGBS import. It is available and relatively cheap.


Kaja Kacperska (HMJV): Are there any special requirements around curing as compared to more standard mixes? Curing into a poured cast in place item is the same, strength build as per OPC depends on heat, no water curing as it dilutes the surface pH that the alkalis are providing. A specific curing compound spray is needed.


QUESTIONS AND ANSWERS


July 2023 | 23


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53