Experimental investigation of effect of admmixture on concrete strength and frost-resistance
The influence of admixture on concrete strength and frost-resistance was analyzed by using the mercury intrusion method and the rapid frozen-thaw method under the condition of the same water/binder ratio in this paper. The results showed that the intensity of the concrete with single doped compound mineral admixture is slightly lower than the normal concrete's in concrete 28-days strength experiment when the fixed water/binder ratio is 0.38, but the extent of the concrete strength growth is bigger, and maybe exceed the normal concrete's at the late period of the whole session. It also could be found that the concrete strength added single air entraining agent is lower, particularly the strength of the concrete double mixed with compound mineral admixture and air-entraining agent is lowest. In term of the pore structure, the porosity rate of concrete can be lower and the harmful hole is decreased as well as the less-harmful hole and no-harmful hole are increased when the compound mineral admixture is mixed. The porosity rate will increase, closed pore and less-harmful hole will enhance by a wide margin if the admixture of air entraining agent is added. Moreover, the pore size distribution of concrete becomes reasonable if these two substances are admixed at the same time. From the aspect of frost-resistance, the concrete with co-doped compound mineral admixture and air-entraining agent is best, the concrete with uni-doped air-entraining agent is better secondarily and the concrete with compound mineral admixture alone is just slightly better.
Effect of Air-Entraining Agent LHD on the Technological Properties of Concrete Mix Containing Superplasticizer S-3
Investigated coeffect of superplasticizer S-3 and air-entraining agents LHD (wood chemical additive) on workability, cohesion and air entrainment of concrete mix. Found that under introducing an additive LHD into the concrete mix comprising supeplastifikator S-3, the mobility of the concrete mix is reduced despite the fact that the additive LHD itself is a plasticizer. Decreased mobility from the introduction 0.1 % LHD makes: slump Abrams - 5-6 %, slump flow - 18-22 %. At the same time LHD additive contributes significantly air entrainment and reduce separating water and mortar. Effect of increasing the connectivity of the concrete mix associated with air entrainment. Regardless of the LHD additive S-3 additive does not reduces water separating, and does not have air-entraining action, and virtually no effect on air entrainment caused by the addition of LHD. With increasing content in the concrete mix additives LHD regardless of dosage S-3 amount of entrained air increases from 3 to 7%, and water separation is reduced to almost 0. Thus, synergy additives S-3 and LHD against plasticize the concrete mix was negative, but a positive effect has been observed in respect of connectivity concrete mix.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.