# Effects of Waste Powders of Tuff Manufactured Sand on Characteristics of Highly Ductile Polyvinyl Alcohol Fiber Engineered Cementitious Composite

## TL;DR

Replacing quartz sand with tuff stone powder in a cement composite improves its strength and ductility, but increases drying shrinkage.

## Contribution

Identifying 40% tuff stone powder replacement as optimal for enhancing mechanical properties of PVA-ECC while reducing harmful pores.

## Key findings

- 40% tuff stone powder replacement maximizes mechanical properties like tensile strain and compressive strength.
- Tuff stone powder reduces harmful pores and improves hydration in the composite.
- Increased tuff stone powder content raises drying shrinkage, which could affect practical applications.

## Abstract

What are the main findings?
The mechanical properties of PVA-ECC are best when the content of tuff stone powder instead of quartz sand is 40%.The incorporate of tuff powder as a replacement for quartz sand can improve the hydration and reduce harmful pores in ECC.The incorporate of tuff powder as a replacement for quartz sand can improve the strain-harding characteristics of ECC.The dry shrinkage of ECC increase with increasing of tuff stone powder content and age.

The mechanical properties of PVA-ECC are best when the content of tuff stone powder instead of quartz sand is 40%.

The incorporate of tuff powder as a replacement for quartz sand can improve the hydration and reduce harmful pores in ECC.

The incorporate of tuff powder as a replacement for quartz sand can improve the strain-harding characteristics of ECC.

The dry shrinkage of ECC increase with increasing of tuff stone powder content and age.

What are the implication of the main findings?
From the perspective of mix proportion optimization for ECC, the identified optimum replacement ratio of 40% for quartz sand with tuff powder provides a clear technical reference for designing high-performance polyvinyl alcohol fiber-reinforced ECC (PVA-ECC). This result substantiates that tuff powder is a viable and effective alternative to conventional quartz sand. Its incorporation enhances the mechanical performance of ECC, promotes cement hydration, and refines the pore structure by reducing the volume of harmful pores. From an engineering application standpoint, this substitution not only reduces reliance on non-renewable quartz sand resources but also contributes to lowering the production cost of ECC.The use of tuff powder as a substitute for quartz sand enhances the strain-hardening behavior of ECC, yet simultaneously intensifies its drying shrinkage with increasing replacement content and curing age. This trade-off is crucial for the rational design and practical application of tuff-modified ECC. The improved strain-hardening performance confirms that tuff powder is a high-performance alternative, enabling ECC to exhibit superior ductility and crack resistance. Consequently, future research should focus on developing synergistic optimization strategies to mitigate shrinkage-induced cracking while maintaining the beneficial strain-hardening characteristics.

From the perspective of mix proportion optimization for ECC, the identified optimum replacement ratio of 40% for quartz sand with tuff powder provides a clear technical reference for designing high-performance polyvinyl alcohol fiber-reinforced ECC (PVA-ECC). This result substantiates that tuff powder is a viable and effective alternative to conventional quartz sand. Its incorporation enhances the mechanical performance of ECC, promotes cement hydration, and refines the pore structure by reducing the volume of harmful pores. From an engineering application standpoint, this substitution not only reduces reliance on non-renewable quartz sand resources but also contributes to lowering the production cost of ECC.

The use of tuff powder as a substitute for quartz sand enhances the strain-hardening behavior of ECC, yet simultaneously intensifies its drying shrinkage with increasing replacement content and curing age. This trade-off is crucial for the rational design and practical application of tuff-modified ECC. The improved strain-hardening performance confirms that tuff powder is a high-performance alternative, enabling ECC to exhibit superior ductility and crack resistance. Consequently, future research should focus on developing synergistic optimization strategies to mitigate shrinkage-induced cracking while maintaining the beneficial strain-hardening characteristics.

In this paper, a highly ductile polyvinyl alcohol fiber engineered cementitious composite (PVA-ECC) was developed by replacing quartz sand (QS) with tuff stone powder (TP) at different replacement ratios of 20%, 40%, 60%, 80%, and 100%. The resulting mechanical properties and drying shrinkage were determined for the developed ECC. Qualitative and quantitative analyses of hydration products, pore structure, and micro-morphology of ECC were conducted by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, pore size and porosity, and scanning electron microscopic imaging. The influencing mechanism of tuff stone powder content on ECC performance was also studied at a micro level. It was found that with the increase in the replacement ratio of tuff stone powder, the ultimate tensile strain and tensile peak stress of ECC all exhibited an increasing trend, which declined afterward. The variation in compressive and flexural strengths also showed a similar pattern. When the replacement ratio of tuff stone powder was 40%, the ultimate tensile strain, peak tensile stress, flexural strength, and compressive strength were higher than the control group by 15.1%, 4.7%, 16.3%, and 10.7%, respectively. When the content of tuff stone powder did not exceed 80%, it could fill the internal pores of the ECC matrix, which reduced harmful pores. With the increase in tuff stone powder content, calcite content increases gradually while the Ca(OH)2 amount decreases. It can be seen that tuff stone powder can improve ECC hydration products. However, incorporating tuff stone powder does not produce new hydration products. Incorporating tuff stone powder increased the drying shrinkage of ECC, and the value of drying shrinkage increased with the increase in the replacement ratio of tuff stone powder.