This article uses the wollastonite from Xiaojipu, Daye, Hubei as the test sample. The X-ray diffraction measurements were compared with the standard powder card for triclinic wollastonite from ASTM, and the main data matched well. Due to the well-developed fibrous crystals of wollastonite produced in Daye, the powder crystals exhibit a two-dimensional distribution, resulting in a higher probability of certain crystal planes appearing while others are less likely to appear. Therefore, some diffraction data for certain crystal planes are missing, and there are differences in diffraction intensity for some individual crystal planes compared to the standard sample.

The infrared absorption spectrum test characteristics are similar to the foreign standard TC-type wollastonite infrared absorption spectrum characteristics, consisting of three absorption bands: the absorption band in the range of 400-500 cm-1 is the absorption band of calcium cation vibrations, the absorption band in the range of 1550-680 cm-1 is the main characteristic absorption band of wollastonite, indicating that the repetition period of the silicate chain is three, and another characteristic absorption band of wollastonite infrared spectrum is in the range of 900-1080 cm-1, indicating the stretching vibration absorption bands of Si-O-Si and O-Si-O.

X-ray diffraction analysis and infrared spectral analysis confirm:

Daye wollastonite belongs to the triclinic chain structure TC-type wollastonite.

The microscopic crystal structure of wollastonite manifests macroscopically as a fibrous structure with a tendency to elongate. Naturally occurring wollastonite is mostly radial, fibrous, feather-like, or formed into blocks by small fibrous aggregates. When it is crushed to 3μ or 8μ, it still appears as fibrous crystals under a scanning electron microscope.

Good processing technology will maintain a good aspect ratio, generally between 7:1 to 5:1. The aspect ratio of naturally occurring wollastonite fibers in China can reach 20:1 to 30:1. This fibrous crystal characteristic provides a special mechanical reinforcement effect for cement mortar, forming a discontinuous mesh-like framework in the cement mortar that acts as reinforcement. When the fibrous crystals are subjected to external forces in cement mortar specimens, they prevent the development of micro-cracks and exhibit crack-blocking effects, demonstrating their mechanical reinforcement capabilities.

Another important factor in improving the mechanical strength of wollastonite cement mortar is the degree of bonding at the interface between wollastonite and the hydration products of cement. According to the theory of cement hydration dissolution and precipitation: hydration ions form on the surface of cement particles and diffuse into the solution. When the solution reaches saturation, ions aggregate to form calcium silicate hydrate crystals. At this point, wollastonite fibers become attachments to the gel, and crystal nuclei begin to form on the surface of wollastonite, gradually growing into crystals. This results in a close crystalline intergrowth between wollastonite and the cement hydration products, leading to a strong interface bond, which gives wollastonite a good reinforcement effect in cement mortar.

Application of wollastonite-reinforced cement mortar in the construction of rural energy biogas pools.

In the past, the materials used for constructing rural biogas pools in China were mostly ordinary concrete, which has poor airtightness. The red mud plastic developed in recent years is prone to aging, insect damage, and rodent bites. The new building material GRC is not only rare but also expensive. To address these issues, we developed a cement mortar made from ordinary Portland cement and slag Portland cement as the base material, combined with abundant and inexpensive natural high-quality fibrous wollastonite, and treated with polymer latex cement composite airtight layers to form a dense, solid, and airtight new building material for pool construction.

The reinforcement effects of different amounts of wollastonite, different particle sizes, different specific surfaces, and different aspect ratios on various types and grades of cement mortar vary. The formulation needs to be optimized through experimental research. The main factors affecting the strength of cement mortar are explained as follows:

1. The effect of wollastonite incorporation on the strength of cement mortar. Using ordinary Portland cement or slag Portland cement as the binding material, fine aggregate quartz sand is added, and the same particle size of fibrous wollastonite is used as the reinforcement material. The same water-cement ratio is controlled, and samples are prepared and tested strictly according to the cement softening standard (GB-177-77). The experimental results show that for the same particle size, different incorporation amounts have different reinforcement effects on cement mortar. When selecting the incorporation amount of wollastonite, the flexural strength of the standard cement mortar increases by 20%, and the compressive strength increases by 33%. In the construction of biogas pools, this study selected a moderate incorporation amount that increased the flexural strength by 18% and the compressive strength by 25%.

2. The effect of different particle sizes of wollastonite on the strength of cement mortar. Within the selected range of wollastonite incorporation amounts, different particle sizes are tested according to the national standard for cement softening (GB177-77). The experimental results indicate that the relationship between the different particle sizes of wollastonite and the reinforcement effect is not linear. The reinforcement effect of different particle sizes depends on the aspect ratio of the wollastonite mineral fibers in each particle size. For the processing technology of Daye wollastonite, the wollastonite with a particle size of 120 mesh to 200 mesh shows better reinforcement effects. Under a microscope, it is statistically observed that 60-85% of the particles have an aspect ratio of 5:1 to 15:1. However, if the particles are too large, the wollastonite appears short and thick, lacking disintegration, resulting in a small aspect ratio and poor flexural strength. When the processing method is incorrect, and the fibrous crystals of wollastonite are damaged, the aspect ratio becomes very small, leading to poor reinforcement effects. A special grinding process is required to minimize fiber length loss, ensuring that wollastonite is finely ground to increase specific surface area while maintaining a large aspect ratio of fibrous crystals for better reinforcement effects.

Conclusion  Summary

Based on the results of laboratory research and the comprehensive technical and economic effects, a formulation was selected to prepare wollastonite-reinforced cement mortar to construct an elliptical thin-shell biogas pool, which was treated with a polymer latex cement composite airtight layer. Ten comparative biogas pools were built at the experimental base in Huangpi County, Hubei Province. It was identified that the new material biogas pool saves labor and resources, is easy to construct, has good airtightness, increases gas production by 30%, and is cost-effective, saving 25 yuan per 6 m3 elliptical concrete biogas pool, reducing costs by 18%.