Overview on Leca® Lightweight Aggregate Concrete (LWAC)
Interview with Geir Norden (Leca® Concrete Specialist)
1. Lightweight aggregate concrete (LWAC) has been used for a long time. One of the earliest uses of reinforced LWAC was in the hulls of ships and barges from around 1918 in the USA. Why is LWAC still an important solution in the infrastructure market today? And what has changed over the last 100 years with LWAC technology?
Geir Norden: Well, we have the same challenges today as 100 years ago. Ships and floaters need to float and to achieve this, lightweight materials achieve better buoyancy. The weight of a concrete structure is still very dependent on the density of the material itself, so lightweight concrete offers a greater advantage. The quality of the LWA has improved significantly during the last 100 years in strength, density, ratio and variation. Today it is simple to make LWAC with a typical compressive strength of 60-70 MPa and still reduce the concrete density by 20-30%. The variations in the quality of the LWA is very low today with uniform and fine pore structure, resulting in standard deviation figures which are lower than for similar normal density concrete, which is remarkable. In addition, the binder system and reinforcement together with the knowledge on LWAC has improved. The largest improvement in recent times is the addition of additives including super plasticizers which make LWAC even more innovative, and this includes LWAC offering self levelling and pumpability for easy delivery to site.
2. Can we compare normal concrete with LWAC, so we can substitute normal concrete with LWAC in every project, in terms of concrete characteristics, price, and sustainability?
Geir Norden: Yes and no. It is possible to substitute all normal weight concrete structures with lightweight concrete, but it is up to the Design Engineer to evaluate the benefits by doing so. It is all in the design, how to design and construct a sustainable structure. The LWA itself costs more than ordinary concrete aggregate, hence this will increase the concrete costs of the LWAC comparable.
From recent projects, my experience tells me that LWAC comes in at a 1.5 to 2 times higher price, depending on the mix design and logistics. It is therefore reasonable to use LWAC where you can find a benefit from the reduced weight and size of the construction. And there are several types of projects. Typical applications are floaters and structures with a long span. Here we can utilize the low weight and reduce the construction costs despite the higher unit price of the LWAC comparable. The LWAC offers good mechanical characteristics and can cover the price differentials when compared to normal density concrete. All designers should be able to calculate and design with LWAC.
Regarding the question on sustainability, the answer is similar; reducing the weight of the structure and being able to construct longer, wider, and slimmer designs, whilst reducing the concrete structure itself, will generate an overall more sustainable structural design.
3. Today, LWAC is widely used across the world as an alternative to normal density concrete (NDC). Can you please mention some of the key projects in recent times where Leca® LWA was used in the design?
Geir Norden: I would like to highlight the Norwegian oil platforms and some of the world’s largest bridges with long spans. This includes the Troll Oil and Gas platform which is a floater and a gravity-based platform with modified light weight concrete in the top shaft. Two recent bridges built in Norway are also highly noteworthy; The Tryssfjord Bridge is a 537m long cantilever bridge with LWAC in the main span. The current development at Nydal bridge in Trondheim is the first structure in Norway where we have pumped LWAC with pre saturated Leca® 800. I would also like to highlight the modern offshore windmill floater that was built in Spain recently by DemoSATH - we believe this structure is groundbreaking for floater design.