## 5 Micro-Properties of the Cemertitious Materials with RP
### Microstructural Analysis
[245] reported the same result stating that the paste with RP demonstrates a significant presence of RP particles enclosed inside substantial C-S-H gels, indicating the nucleation and filling actions of RP. [PERSON] et al. [295] reported that within a mixture containing 30% ground concrete powder (GCP), a robust and efficient bonding interaction is seen between GCP particles and recently generated hydration products. Nevertheless, substituting 70% of the cement with GCP has a detrimental impact on the formation of microstructure, as well as a weak adhesive interaction between the GCP particles and C-S-H gels. [PERSON] et al. [140] and [PERSON] et al. [217] reported that when 30% of RCP was utilized as a substitute for cement, the matrix structure exhibited increased roughness, accompanied by the presence of many pores and the observation of hexagonal flake CH. They also reported that the RCP-2%NS group exhibited a denser microstructure with fewer cracks and pores compared to the RCP group, due to the beneficial impact of NS on cement hydration. Thermal activation, CO\({}_{2}\) activation, chemical activation, biomineralization, and nano activation provide a denser structure and a good bonding capacity between the RP particle and new hydration products in RP blended mixtures [81; 83; 84; 100; 205; 222; 231; 256; 299; 300]. [PERSON] et al. [97] reported that the inclusion of the RP did not appear to modify the structure of the alkali-activated cement. Nevertheless, further microcracks emerged, and a portion of the RP became embedded within the recycled alkali-activated cement (RAAC) matrices. They also conducted tests on RP-integrated paste with various activation temperatures. They stated that the heating pretreatment of RP had a slight impact on the shape of the alkali-activated cement produced. The microstructure of RAAC10%-T600C exhibited a high level of compaction and density, with the matrix containing porous structures of the RP and spherical FA. On the other hand, RAAC10%-T800C exhibited a less uniform microstructure characterized by an increased number of cracks inside its matrix. [PERSON] et al. [8] stated that at temperatures ranging from 300 \({}^{\circ}\)C to 900 \({}^{\circ}\)C, the microstructure of the paste including thermally modified WCP is more compact than the paste containing untreated WCP. Additionally, the thermally modified WCP particles are surrounded by a dense layer of C-S-H. However, the micro-structure of paste containing 1200 \({}^{\circ}\)C-modified WCP becomes less dense and more porous compared to other pastes. [PERSON] et al. [101] reported that, at a substitution level of 50%, the micro-structure of paste with 50% heat-modified WCP is denser compared to paste with 50% un-modified WCP. [PERSON] et al. [263] stated that the morphology of ettrinigite in the control sample containing 0% CRCF is more elongated compared to the ones created in cement paste with CRCF. Furthermore, the length of ettrinigite reduces as the level of CRCF increases. The SEM images of the sample containing 30% CRCF do not exhibit the presence of \"needle-like\" particles. This result suggests that CRCF has the ability to undergo a reaction with ettrinigite. The sample containing 30% CRCF exhibits a microstructure that is denser and less porous compared to the control sample. [PERSON] et al. [130] investigated the impact of CRCF on the initial hydration kinetics of OPC paste. They reported that when the CRCF particle encounters water, the surface of the particle quickly becomes coated with many needle-shaped C-S-H gels. They stated that the CRCF10 paste demonstrates a microstructure that is more uniform and compact compared to the reference paste, particularly at 3 d. This phenomenon can be attributed to the increased formation of C-S-H hydrates and other hydrates caused by the accelerated growth of C-S-H seeds in the CRCF10 paste, resulting in a filling effect.