In order to study the effect of metakaolin on the water resistance of magnesium phosphate cement mortar, we took four factors as research objects: the setting time, fluidity, compressive strength, and water resistance of magnesium phosphate cement mortar. These were studied after adding equal gradations of metakaolin, and we then carried out SEM microcosmic experiments on the best group. The results showed that with the increase in metakaolin content, the setting time of magnesium phosphate cement decreased gradually, and the fluidity of the mortar decreased as a whole. The effect of metakaolin on the fluidity of the magnesium phosphate cement mortar was not significant when the content of metakaolin was less than 8%. Metakaolin was able to improve the pore structure of magnesium phosphate cement mortar; for example, it improved its compressive strength and water resistance due to both chemical and physical interactions. The water resistance of mortar samples in the same timeframe increased first and then decreased with the increase in metakaolin content. When the content of metakaolin was 12%, the water resistance of magnesium phosphate cement mortar achieved the optimal results. A 50.32% improvement of the 56 d strength retention rate and a 54.89% improvement of the 90 d strength retention rate proves its effective long-term water resistance.

In Shanxi Province, China, concrete foundations of substations are widely exposed to environments with sulfate erosion, which results in severe damage. There are various avenues to enhance sulfate resistance, and one promising approach involves optimizing high-performance water reducers. Chain extender, which is an integral component of a water reducer, serves as a pore-blocking agent to effectively counter sulfate erosion. This study delves into the impact of a chain extender in the water reducer on the sulfate resistance and adaptability of ordinary concrete. The assessment begins with gauging the sensitivity of concrete to sulfate erosion, utilizing a 0–1 scoring method. Comparable conditions are maintained, allowing for a direct comparison between concrete with and without chain extender based on predefined criteria. A score of 1 denotes superior performance, while a score of 0 indicates a poorer performance. Following the evaluation of each criterion, scores are aggregated by the water reducer type, with higher scores signaling superior adaptability. The findings highlight that chain extender enhances the internal porosity of concrete, resulting in a more compact microstructure, heightened impermeability, and improved resistance to sulfate erosion. Its influence on mixture performance, however, is marginal. From an erosion product standpoint, using the semi-immersion method, chemical erosion predominates in the immersion zone, while both chemical and physical erosion are observed in the alternate wet–dry zone. Employing a 0–1 scoring method, Water Reducer 3^# (with chain extender) scores 20 points, whereas Water Reducer 3^#–1 (without chain extender) scores 4 points. Taking into consideration all factors, the chain extender demonstrates excellent adaptability to ordinary concrete. To validate the effectiveness of the 0–1 scoring method, it is applied to assess fly ash and slag double-blended concrete. Water Reducer 3^# (with chain extender) scores 13 points, while Water Reducer 3^#–1 (without chain extender) scores 10 points. Taking all aspects into consideration, the chain extender component exhibits commendable adaptability to fly ash and slag double-blended concrete.