# Laboratory and Full-Scale Tests of Modern Chimney Casings Based on Lightweight Perlite Concrete with Hydrophobic Admixtures

## TL;DR

Researchers tested lightweight perlite concrete with hydrophobic additives to improve chimney casings, finding that these additives effectively reduce moisture absorption while maintaining structural strength.

## Contribution

The study introduces optimized hydrophobic admixtures for perlite concrete to meet strict moisture and strength requirements for chimney casings.

## Key findings

- Hydrophobic admixtures significantly reduced water absorption and capillary uptake in perlite concrete.
- Concrete mix achieved required bulk density and compressive strength while maintaining moisture resistance.
- Production line tests confirmed the effectiveness of the optimized mix under real-world conditions.

## Abstract

Currently, chimney technology is looking for new materials with improved thermal insulation properties and, at the same time, adequate durability. The use of concretes based on lightweight aggregates, such as expanded perlite, is capable of meeting such a challenge, provided that the composition of the concrete mixes is appropriately modified. The main research challenge when designing chimney system casing elements lies in ensuring adequate resistance to moisture penetration (maximum water absorption of 25%), while achieving the lowest possible bulk density (below 1000 kg/m3), sufficient compressive strength (minimum 3.5 MPa), and capillary water uptake not exceeding 0.6%. In the present research, laboratory tests were conducted to improve the fundamental technical properties of lightweight perlite-based concrete to meet the aforementioned requirements. Laboratory tests of perlite concrete were carried out by adding eight chemical admixtures with a hydrophobic effect and the obtained results were compared with a reference concrete (without admixtures). However, the positive results obtained under laboratory conditions were not confirmed under actual production conditions. Therefore, further tests were conducted on chimney casings taken directly from the production line. Subsequent chemical admixtures with a hydrophobic effect, based on silane/siloxane water emulsions, were applied to determine the concrete mix’s optimal composition. The results of the tests carried out on perlite concrete chimney casings from the production line confirm the effectiveness of the applied chemical admixtures with a hydrophobic effect in improving the moisture resistance. This was further supported by the outcomes of the so-called ‘drop test’ and capillary uptake test, with the suitable bulk density and compressive strength being maintained.