1) Improving the strength of cement slurry and mortar is one of the hallmarks of high performance of concrete. One of the main purposes of adding metakaolin is to improve the strength of cement mortar and concrete.

Poon et al, Its strength at 28d and 90d is equivalent to that of metakaolin cement, but its early strength is lower than the benchmark cement. Analysis suggests that this may be related to the severe agglomeration of the silicon powder used and insufficient dispersion in the cement slurry.

(2) Li Keliang et al. (2005) studied the effects of calcination temperature, calcination time, and SiO2 and A12O3 content in kaolin on the activity of metakaolin to improve the strength of cement concrete. High strength concrete and soil polymers were prepared using metakaolin. The results show that when the content of metakaolin is 15% and the water cement ratio is 0.4, the compressive strength at 28 days is 71.9 MPa. When the content of metakaolin is 10% and the water cement ratio is 0.375, the compressive strength at 28 days is 73.9 MPa. Moreover, when the content of metakaolin is 10%, its activity index reaches 114, which is 11.8% higher than the same amount of silicon powder. Therefore, it is believed that metakaolin can be used to prepare high-strength concrete.

The axial tensile stress-strain relationship of concrete with 0, 0.5%, 10%, and 15% metakaolin content was studied. It was found that with the increase of metakaolin content, the peak strain of axial tensile strength of concrete significantly increased, and the tensile elastic modulus remained basically unchanged. However, the compressive strength of concrete significantly increased, while the compressive strength ratio correspondingly decreased. The tensile strength and compressive strength of concrete with a 15% kaolin content are 128% and 184% of the reference concrete, respectively.
When studying the strengthening effect of ultrafine powder of metakaolin on concrete, it was found that under the same fluidity, the compressive strength and flexural strength of mortar containing 10% metakaolin increased by 6% to 8% after 28 days. The early strength development of concrete mixed with metakaolin was significantly faster than that of standard concrete. Compared with the benchmark concrete, the concrete containing 15% metakaolin has an 84% increase in 3D axial compressive strength and an 80% increase in 28d axial compressive strength, while the static elastic modulus has an 9% increase in 3D and an 8% increase in 28d.

The influence of mixed proportion of metakaolin soil and slag on the strength and durability of concrete was studied. The results show that adding metakaolin to slag concrete improves the strength and durability of the concrete, and the optimal ratio of slag to cement is around 3:7, resulting in ideal concrete strength. The arch difference of composite concrete is slightly higher than that of single slag concrete due to the volcanic ash effect of metakaolin. Its splitting tensile strength is higher than that of the benchmark concrete.

The workability, compressive strength, and durability of concrete were studied by using metakaolin, fly ash, and slag as substitutes for cement, and mixing metakaolin with fly ash and slag separately to prepare concrete. The results show that when metakaolin replaces 5% to 25% cement in equal amounts, the compressive strength of concrete at all ages is improved; When metakaolin is used to replace cement by 20% in equal quantities, the compressive strength at each age is ideal, and its strength at 3d, 7d, and 28d is 26.0%, 14.3%, and 8.9% higher than that of concrete without metakaolin added, respectively. This indicates that for Type II Portland cement, adding metakaolin can improve the strength of the prepared concrete.

Using steel slag, metakaolin, and other materials as the main raw materials to prepare geopolymer cement instead of traditional Portland cement, in order to achieve the goal of energy conservation, consumption reduction, and turning waste into treasure. The results show that when the content of steel and fly ash is both 20%, the strength of the test block at 28 days reaches very high (95.5MPa). As the amount of steel slag added increases, it can also play a certain role in reducing the shrinkage of geopolymer cement.

Using the technical route of “Portland cement+active mineral admixture+high-efficiency water reducing agent”, magnetized water concrete technology, and conventional preparation processes, experiments were conducted on the preparation of low-carbon and ultra-high strength stone slag concrete using raw materials such as stones and slag from a wide range of local sources. The results indicate that the appropriate dosage of metakaolin is 10%. The mass to strength ratio of cement contribution per unit mass of ultra-high strength stone slag concrete is about 4.17 times that of ordinary concrete, 2.49 times that of high-strength concrete (HSC), and 2.02 times that of reactive powder concrete (RPC). Therefore, ultra-high strength stone slag concrete prepared with low dosage cement is the direction of concrete development in the low-carbon economy era.

(3) After adding kaolin with frost resistance to concrete, the pore size of the concrete is greatly reduced, improving the freeze-thaw cycle of the concrete. Under a certain number of freeze-thaw cycles, the elastic modulus of the concrete sample with a 15% kaolin content at 28 days of age is significantly higher than that of the reference concrete at 28 days of age. The composite application of metakaolin and other mineral ultrafine powders in concrete can also greatly improve the durability of concrete.