Combined treatment improves recycled aggregate in laboratory tests

Jingyu Yang and seven coauthors reported on September 26, 2026, in Construction and Building Materials that a combined surface treatment improved several measured properties of recycled aggregate. The result addresses a problem for reusing material from old concrete: it can absorb more water and resist crushing less effectively than natural aggregate. The published university record describes tests on aggregate and its interaction with cement paste, leaving open how concrete made with the treated material would perform in a structure.

Which treatment performed best?

The researchers compared three approaches: pozzolan slurry alone, sodium silicate with silane, and a treatment combining all three components. They examined the aggregate's physical and mechanical properties, then studied how the treated material interacted with cement paste. In the study's account, the combined pozzolan slurry, sodium silicate and silane treatment gave the best overall performance among those tested. The authors said it made the aggregate surface more uniform and filled most of its original surface pores.

Compared with untreated aggregate, the combined treatment reduced measured water absorption by 29.01% and the crushing value by 43.06%, according to the authors. They also reported porosity reductions ranging from 18.35% to 44.36%. Those figures describe changes in the material tested, rather than the strength or service life of concrete containing it. The abstract also lists a 3.27% reduction in apparent density among the combined treatment's results, without explaining why that particular change is counted as an improvement.

How did the other treatments compare?

The sodium silicate and silane treatment formed what the authors described as a uniform protective film over the aggregate surface. It reduced porosity and water absorption, but its improvement in crushing value was limited. Pozzolan slurry on its own made the surface more uniform while leaving some areas partly uncovered. For that treatment, the authors reported porosity reductions of 6.30% to 14.83% and a 27.77% reduction in crushing value.

Why does cement paste interaction matter?

Aggregate sits within cement paste in concrete, so a change to its surface is relevant beyond the aggregate's own measurements. The September study reports lower contact angles with cement paste for all three treated aggregates than for untreated material. It also found that the influence of aggregate water absorption on paste infiltration diminished as the paste's water-to-cement ratio increased. The amount of paste adsorbed by the aggregate fell as the aggregate's water content rose.

Those results indicate that moisture in the aggregate and in the paste affected the interaction measured by the researchers. They do not show that any one treatment will produce a specified concrete strength in a building. The accessible publication record provides the abstract, rather than a readable full paper with sample sizes, uncertainty ranges and the detailed test conditions needed to assess how broadly the measurements apply.

The established obstacle for recycled concrete aggregate

A separate 2024 review by Faisal Muhammad and colleagues helps explain why these measurements are relevant. It found that mortar remaining attached to recycled concrete aggregate can be porous, absorb substantial water and contribute to variation in material quality. In the literature the review assessed, concrete made with recycled aggregate generally showed lower resistance to crushing, impact and abrasion than concrete made with natural aggregate. Its properties also tended to deteriorate as the recycled aggregate share increased.

That earlier review did not test Yang and colleagues' new treatment. It describes the wider challenge the treatment is intended to address: changing a recycled aggregate's surface may improve a troublesome material property, while the properties of the finished concrete remain a separate question. Variation among sources of recycled aggregate, identified in the review, is another reason results from a tested material cannot automatically be applied to every demolition stream.

What remains to be established for building use?

The reported improvements make the combined treatment a candidate for further testing, but the accessible September abstract does not report full-scale structural performance, field durability or compliance with building requirements. Tests of concrete made with treated aggregate would be needed to assess those questions. The record also does not establish treatment cost or whether its energy use and emissions would leave an environmental advantage across the supply chain. For now, the strongest supported conclusion is narrower: in the reported aggregate tests, the combined treatment produced the best overall measured improvement of the three methods.