# Lightweight, Heat-Insulating, Alkali-Activated Slag Composites with Carbon-Based Biochar Additive and Filler

## TL;DR

This paper shows that adding biochar waste to alkali-activated slag improves strength and insulation properties, with optimal performance at 0.25% biochar.

## Contribution

The study introduces biochar waste as a novel additive and filler in alkali-activated slag composites, enhancing mechanical and insulation properties.

## Key findings

- Samples with 0.25% biochar waste achieved the highest compressive strength of 44.4 MPa.
- Biochar waste improved thermal and acoustic insulation properties of the composite.
- SEM analysis confirmed good adhesion between biochar waste and the alkali-activated slag matrix.

## Abstract

What are the main findings?
Biochar waste (BW) was made from waste wood.A small amount of BW (>0.5%) was used as an additive, while a larger amount (1–25%) was used as a filler.Samples with 0.25% of BW exhibited the highest compressive strength (44.4 MPa).

Biochar waste (BW) was made from waste wood.

A small amount of BW (>0.5%) was used as an additive, while a larger amount (1–25%) was used as a filler.

Samples with 0.25% of BW exhibited the highest compressive strength (44.4 MPa).

What are the implications of the main finding?
Based on SEM findings, BW had good adhesion with the alkali-activated slag matrix.The thermal and acoustic insulation effect of the samples increased with the addition of BW.

Based on SEM findings, BW had good adhesion with the alkali-activated slag matrix.

The thermal and acoustic insulation effect of the samples increased with the addition of BW.

An alkali-activated slag binder based on biochar was developed in this research. The biochar was produced from waste wood and is referred to as biochar waste (BW). In the alkali-activated slag system, a small amount of biochar (up to 0.5%) was used as an additive, and a larger amount (from 1% to 25%) was used as a filler. The influence of the biochar powder on compressive strength was determined. The hydrated samples were investigated using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), and the thermal, acoustical properties, and hydration temperature were also determined. The compressive strength of the alkali-activated slag composite, especially after 7 days, was found to increase slightly due to the introduction of a small amount (0.05–0.5%) of BW powder. The powder in the alkali-activated slag matrix was distributed homogenously, resulting in a reduction in the crack propagation. A larger amount of BW led to a non-homogeneous distribution, and this resulted in a gradual reduction in compressive strength with increasing BW. The highest values of compressive strength at 28 days of hydration (44.4 MPa) were recorded for samples with 0.25% of BW. According to mathematical analysis methods, the compressive strength is mainly influenced by the specific surface area of the initial mix ingredients and the amount of BW additive. In the alkali-activated slag matrix, BW acted as an inert micro-filler, with the dilution effect possibly being the reason for the decrease in the hydration temperature. SEM analysis demonstrated that the BW had a good adhesion with the alkali-activated slag matrix. The thermal and acoustic insulation performance of samples with BW improved. These investigations suggest that BW can be successfully incorporated in alkali-activated material, resulting in low thermal conductivity and adequate acoustic insulation performance.