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In this work, we report for the first time the applications of cationic oligomeric surfactants as novel air entraining agents for concrete. A series of oligomeric surfactants with the oligomerization degrees from 2 to 4 was synthesized. Using them as the air entraining agents, the surface activity and foaming properies were tested in both water and cement filtrate. The air contents and air-void parameters were also tested in both cement mortars and concretes. The results show that the oligomeric surfactants have higher performance compared with their monomeric analogue and traditional air entraining agents, and the surfactant with higher oligomerization degree has higher performance. The surfactants are also beneficial for the durability of concrete, and could only affect the strength of concrete slightly. Our studies indicate great potential of the oligomeric surfactants for practical applications.

This study aims to investigate the autogenous shrinkage-reducing mechanisms of the novel polymer-type shrinkage-reducing admixture (SRA) with water-reducing function. For comparison, the traditional polyether-type SRA was also used. The development of autogenous deformation, hydration rate, internal relative humidity (RH), electrical resistivity, ions and SRAs concentration in pore solutions and crystal content of cement pastes were comprehensively investigated. Unlike the polyether-type SRA mixture which has an expansion period at early age, a relatively slow and monotonous evolution of shrinkage was observed for the polymer-type SRA mixture. It is concluded that the delay and regulation effects on cement hydration of the novel SRA obviously influence the microstructure development and the evolutions of various performances of cement pastes comparing to the polyether-type SRA. Furthermore, both the self-desiccation status induced capillary pressure and the crystallization pressure induced expansion stress contribute to the shrinkage-reducing behaviors of SRAs on the autogenous deformation of the cement pastes.

The development of high performance air entraining agents for concrete is of great importance. In this work, gemini surfactants (a new class of surfactants) have been utilized as air entraining agents for the first time. Three gemini surfactants modified with different anionic groups (sulfonic, sulfate and phosphate groups) were designed and synthesized. The surface tensions and foam heights of their solutions were tested. Using them as the air entraining agents, the air contents and air-void parameters of the cement mortars were tested. The study results clearly show that the gemini surfactants have higher surface activity, foamability, foam stability and air entraining performance compared with the corresponding single-chained surfactants, and the sulfate group modified gemini surfactant has the highest performance. These surfactants are tested merely as model compounds; however, they show higher air entraining ability compared with the benchmark surfactants used in the industry, indicating great potential for practical applications.

The development of high performance air entraining agents for concrete is of great importance. In this work, sulfonic gemini surfactants have been utilized as high performance air entraining agents for the first time. Six sulfonic gemini surfactants with different hydrophobic chains and spacer groups were designed and synthesized. The surface tensions and foam properties of their aqueous solutions were tested. Using them as the air entraining agents, the air contents and air-void parameters of the cement mortars were also tested. The properties of different geminis and their single-chained analogue were fully compared and discussed. The results show that the geminis have higher surface activity, foamability, foam stability and air entraining performance compared with their single-chained analogue, and the gemini with 12-carbon hydrophobic chains and 2-carbon alkyl spacer has highest performance.

In this work, the effects of the charge density of the anionic copolymers on the properties of fresh cement pastes were fully discussed. A series of random copolymers based on anionic acrylic acid (AA) and nonionic N, N-dimethyl acrylamide (DMAA) were prepared by free radical solution polymerization. By varying the initiator concentration, the obtained polymers have different charge densities but similar molecular weights. The adsorption, fluidity, bleeding and rheology of the cement pastes mixed with different polymers were tested, respectively. The results indicate that the anionic and nonionic monomer of the polymers effect on the properties of fresh cement paste cooperatively, and the polymer with medium charge density can effect on the cement paste strongest. Our study is quite beneficial to understand the structure–property relationships and action mechanism of anionic polymers in cement pastes.

In this paper, the effect of salts in solution and the adsorption of surfactant are studied to give the answer why the air entraining agents fail. The high valence cations (e.g. Ca2+) weaken the surface activity of anionic surfactant solution but have no effect on the surface activity of cationic and nonionic surfactant solution. The calcium induces the decreased surface activity of anionic surfactant solution, the low foamability, the big bubble size, and the depressed the air-entraining performance. Anionic surfactant has stronger adsorption on surface of cement than that on surface of montmorillonite, granite and limestone. But cationic and nonionic surfactants have much stronger adsorption on surface of montmorillonite and granite than that on surface of cement. When montmorillonite, granite and limestone are added into cement mortar, the air-entraining performance of anionic surfactant is not depressed, but the air-entraining performance of cationic and nonionic surfactants are obviously depressed.

Entraining tiny and stable bubbles into cement and concrete is becoming more and more important with the complex composition of cement and concrete. In this work, multi-component surfactants are compounded to improve the air-void stability in fresh concrete. The surface tensions, foam properties of their solutions, and the air contents and air-void parameters of the fresh and hardened cement mortars were tested. The results show that there are strong interactions on the interface of multi-components by calculating the important parameters of surface activity. When coconut diethanol amide molecules are introduced into the interface for co-assembly, the electrostatic repulsion between the anionic surfactant molecules is effectively diminished, thereby decreasing the interfacial free energy and making the interface more stable. The multi-component surfactants induced smaller bubbles with larger amounts in aqueous solutions, which also have higher stability of air bubbles in both cement mortars and concretes. So it is of great practical significance to compound nonionic and anionic surfactants to improve the air-void stability in concrete.