Preparation of a tuff polymer and the mechanism of alkaline solution influences on compressive strengths

To promote the effective utilization of the tuff powder waste, this paper proposes a preparation method for a tuff polymer. The raw material is the by-product in the machine-made tuff-based aggregate production process. NaOH and Na₂SiO₃ were added to the raw material successively and cured in an airtight condition at 60 ℃. Compared to the production of Portland cement, higher temperature excitation was not necessary, and lower carbon dioxide emissions during the chemical reaction were achieved. Based on the compressive strength, pH value, scanning electron microscopy, X-ray energy dispersive spectrometer, X-ray diffraction spectrogram, and Fourier transform infrared spectroscopy tests on samples with a variety modulus (n(SiO₂)/n(Na₂O)) of the activator, the mechanism of the modulus of activator influences on the compressive strengths of this tuff polymer was investigated. This work highlights the following: (1) A superior mechanical performance was observed. Results revealed that the optimum modulus was 0.042–0.055 at a range of 0.034–0.150, and the corresponding maximum strength of the tuff powder was 71.33 MPa. (2) The comprehensive microscopic characterization proved the mechanism of strength development. Microscopic characterization results revealed that the alkali activator mainly acted with the surface of tuff powder particles. With the decrease of the modulus of the activator, the dissolution extent of particles increased, and more aluminosilicate was produced, resulting in strength development. When the modulus was below the optimum value, defects such as pore diameter increased, and the contacting area of the polymer on the surface of the tuff particles decreased, resulting in strength deterioration. When the modulus of the activator was 0.150 and 0.080, the strength development occurred between three and seven days. When the modulus of the activator was 0.050, 0.042, and 0.034, the strength development mainly occurred between 7 and 14 days. The pH value variety of the leaching solution generally corresponded to strength development. The increased strengths are attributed to the consumption of OH⁻ in the polymerization and polycondensation stages. Meanwhile, a pH value that is too high may result in depolymerization of the production in the polymerization and polycondensation stages. In addition, the electrostatic repulsion increased, and therefore the strengths of the tuff polymer decreased.