Geopolymers possess good mechanical properties and durability, and their partial replacement of traditional Portland cement is noteworthy for promoting the development of low-carbon building materials. To clarify the influence mechanism of the mechanical properties of slag-fly ash-based geopolymer mortar, this paper investigated the hydration heat, composition, and morphology of hydration products with various contents and moduli of waterglass. The results showed that the compressive strength of geopolymer mortar increased with increasing waterglass content, and first rose and then fell as the waterglass modulus raised, while its flexural strength increased and then decreased with the growth in both. The compressive and flexural strength of geopolymer mortar with 1.2-modulus waterglass at 20 wt% cured for 28 days were 88.4 MPa and 9.0 MPa, respectively. The hydration temperature and cumulative hydration heat of geopolymer mortar was elevated with the increase in waterglass content, and declined with the rising waterglass modulus. The hydration products of the geopolymer consisted of dense amorphous and flocculent structures wrapped around each other. The microstructure of the geopolymer cured for 3 days was loose when the content of 1.4-modulus waterglass was 5 wt%. The relative areas of the flocculation in the geopolymer cured for 28 days increased while the waterglass modulus was greater than 1.4, forming an interface with the dense amorphous structure generated during the early hydration stage, leading to a decrease in its mechanical properties. Therefore, it is recommended for slag-fly ash geopolymer mortar that the waterglass modulus is between 1.2 and 1.4 and its content is no less than 10 wt% to ensure suitable mechanical properties. This study also provided a referenceable time period for the pouring and operation of the engineering application of slag-fly ash-based geopolymer repair mortar.

The short-term creep properties of cracked soft rock are the basis for analyzing and predicting the long-term deformation characteristics of engineering rock mass. Based on orthogonal test design and by means of physical testing and theoretical analysis, this paper systematically studies the short-term creep strain properties of soft rock mass with a vertical anchor form under different combinations of crack number, crack discontinuity degree and crack inclination. The results show the following: (i) as the stress increases, the growth rate of the instantaneous strain of the anchored soft rock slows down, the growth rate of the creep strain increases and the growth rate of the total strain decreases at first and before it then increases. Based on this, the idea is proposed that the stress corresponding to the turning stress of the total strain change rate, from small to large, is the turning stress of the strain rate. This stress value is approximately 50% of its uniaxial compressive strength (UCS). (ii) Statistical analysis shows that for the same cracked rock mass, the three characteristics of cracks have different effects on the instantaneous strain, creep strain and total strain of anchored soft rock, and a certain number of cracks under specific geometric conditions are beneficial to the long-term deformation control of anchored soft rock. (iii) A relative creep model based on mutation is proposed. Considering the effects of the test instrument, the model can be divided into the power function model, the logarithmic function model and the exponential function model, according to goodness of fit. All three models can describe the initial and stable creep stage of anchored soft rock with cracks.

In this paper, a biaxial compression experimental study of NPR (negative Poisson’s ratio) and PR (Poisson’s ratio) anchored rock under different burial depth conditions was conducted around a new type of constant resistance large deformation anchor cable, also known as NPR anchor cable. A comparative analysis was performed on mechanical characteristics of the two types of anchored rock. Furthermore, a concept of static toughness for anchored rock was established to evaluate the comprehensive mechanical performance. The results indicate that with increasing confining pressure, the elastic modulus of both types of anchored rock exhibits a gradual increase. The peak strength and residual strength initially decrease and then increase. The NPR anchored rock has higher elastic modulus, peak strength, and residual strength compared to PR, with increases of 17.5%, 26%, and 25%, respectively. As the confining pressure increases, the fine and short shear cracks within the lateral surfaces of the two types of anchored rock transform into wider and longer cracks. The final integrity of the NPR anchored rock is demonstrably superior to that of the PR. Compared to PR, the cumulative energy, cumulative count, and energy value per unit count of the NPR anchored rock throughout the experiment are significantly lower values. A calculated analysis revealed that the static toughness of the NPR anchored rock is considerably greater than that of PR.