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.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.