Use of recycled concrete and lime to improve marginal subgrades in the Toowoomba Regional Council

Brennan, Matthew Aaron (2016) Use of recycled concrete and lime to improve marginal subgrades in the Toowoomba Regional Council. [USQ Project]

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Toowoomba Regional Council (TRC) is responsible for maintaining the road network within its boundaries. Of the 9650 km 3330 is sealed pavement. Most importantly for pavement design is the quality of the foundation/host soil (Subgrade), of which the pavement will be constructed upon. Pavement thickness is determined directly from the subgrade strength in terms of California bearing ratio (CBR). High strength subgrades (CBR>5) can significantly reduce construction/maintenance cost in comparison to a marginal subgrade (CBR<5). Chemical stabilization with lime can be used to improve the load bearing qualities of marginal subgrades. Mechanical stabilization (i.e. blending of materials) can also be used to compensate shortcomings in the host soils characteristics. This is mostly achieved by redefining the particle size distribution of the host material, providing better particle interlock. This project looks at the use of lime and recycled concrete aggregate (RCA) to improve marginal subgrades and the effect on cost.

With a set budget each financial year, council aims to construct and maintain road pavements as efficiently and in the most cost effective way, to ensure satisfactory pavement performance. Cost effective alternatives are important to achieve this goal. Lime treatment in the civil engineering discipline is not new technology; however its use with recycled concrete aggregate has not been researched. Lime treatment alone is not common practise in TRC; the results of this project will add to council knowledge and may promote more lime treatment to be used as an alternative solution.

Quantitative research methodology was utilized to explore the effect of various lime and RCA contents on two host subgrade materials. The subgrade materials were sampled from Mann Silo Road and Hinz Street, both within TRC Borders. In preparation of the paper, many hours of laboratory testing and preparation was conducted on the samples. This involved site sampling of subgrade from the two roads, initial testing/characterisation, treatment with lime and RCA, curing, final testing and results/cost analysis. Some Pavement redesigns using the mechanistic pavement design was conducted for the host roads. In addition to this a cost analysis with council unit rates was also preformed to consider the application of RCA/Lime treatment as a viable alternative.

Background literature in regards to lime treatment has been thoroughly examined, along with current industry standards and manuals. Initial testing of the host materials shows that they are in acceptable ranges for lime treatment. The addition of lime saw the Host materials CBR increase by a factor of 10. The addition of RCA saw further increases to a factor of 15. Parallel with literature, it’s found that lime increases soil strength and can reduce construction costs. These outcomes were achieved by applying standard soil testing and cost analysis/estimation technique currently used by local government council.
Lime treatment of marginal subgrade is a viable alternate for construction and maintenance of roads. It can return cost savings in construction and maintenance operations. Effect of lime content on in-situ moisture content is also a valuable finding, In addition to this, the effect of RCA is also significant finding. This paper does not aim to solve any major issue but aims to express to council the viability of lime treatment. Toowoomba Regional Council must be thanked for providing me with resources, advice and assistance on the delivery of this project.

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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Honours) (Civil) project
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Nataatmadja, Andreas; Casagrande, Angelo
Date Deposited: 19 Jul 2017 01:45
Last Modified: 19 Jul 2017 04:12
Uncontrolled Keywords: recycled concrete and lime; marginal subgrades
Fields of Research (2008): 09 Engineering > 0905 Civil Engineering > 090503 Construction Materials
Fields of Research (2020): 40 ENGINEERING > 4005 Civil engineering > 400505 Construction materials

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