Background

Accounting for about 60% of concrete, coarse aggregate has been regarded as an essential ingredient, demanded by constructions in building and construction sector(B&C). However, with high-quality natural aggregate depleting and national environmental policies restricting, modified treatment to inferior coarse aggregate was put forward to address the challenge of aggregate shortage in B&C. 

Compared with regular aggregate, inferior coarse aggregate with porous surface and particle morphology is characteristic of low strength and density, high water absorption, high adsorption to water-reducing agent and other shortcomings. Applying inferior coarse aggregate into construction directly may lead to serious problems.

Key properties from lab test

The polymer modifier was developed and applied to impregnate and fill the pores or cracks, thus improving the soundness of aggregate by 67%. On the other hand, polymer modifier forms a hard protective shell, which serves to optimize particle morphology of inferior aggregate, enhancing permeability resistance, and lowering water absorption ratio as well as adsorption to water-reducing agent by over 80%, compared with that of untreated aggregate.
 

 

Comparison of modified and untreated aggregate

Compressive strength of modified and untreated aggregate concrete 

Demonstration

The demonstration of polymer modified inferior coarse aggregate was implemented in the maintenance of the Liaocheng section on Beijing-Kowloon Railway. According to the demonstration, the performance of concrete with polymer modified inferior coarse aggregate is equivalent to that of regular aggregate. Besides, the appearance of sleeper is highly similar to conventional one, with 1d, 14d, and 28d compressive strength increased by 16%, 7% and 8% respectively. Meanwhile, the result of static load and fatigue test satisfied the requirements.

Waste is a misplayed resource

In terms of economic performance, the cheap inferior coarse aggregate, which was discarded or landfilled as waste in the past, will significantly cut construction costs. Meanwhile, the issues arose from aggregate supply could be mitigated in some regions which lack high-quality aggregate.

As for the environmental benefit, with the efficient utilization of inferior coarse aggregate, the exploitation of natural aggregate can be greatly reduced while the land and resources required in solid waste disposal could be saved, which is environmentally friendly. 

Durability of polymer modified inferior coarse aggregate will be studied ing the next stage,and more demonstrations of modified aggregate concrete sleeper will be followed.

Project PI