1. test raw materials and test methods
1.1 raw materials
Cement(28d strength 54.2 mpa),Fly ash,Mineral power,Coarse aggregate(5-31.5mm gravel),fine aggregate: manufactured sand, fineness modulus 2.8, HPMC: viscosity: 30000(MK20M), 100000(MK50M), 200000(MK70M) (here after expressed as hpmc-3w, hpmc-10w, hpmc-20w); Additive: polycarboxylate superplasticizer.
1.2 test method
The test is carried out according to the relevant provisions of test method for performance of ordinary concrete mixture (GB / T50080-2016), mechanical test method for ordinary concrete (GB / T50081-2002) and standard for test method for basic performance of building mortar (JGJ / T70-2009). In the water retention test, 2.36mm square hole sieve is used to screen out the particles larger than 2.36mm.
1.3 test mix proportion (see Table 1)
Table 1 Raw materials and mix proportion of concrete kg.m-3
2. Results and discussion
2.1 effect of cellulose ether on slump and expansion of concrete (see Figure 1-2)
Figure1 effect of cellulose ether on slump Figure 2 effect of cellulose ether on expansion of concrete
The first is to increase the viscosity of fresh concrete and increase the cohesiveness, which makes the shear force of concrete increase during the flow process, which leads to the decrease of slump and expansion of concrete.
The second is to introduce tiny bubbles, which play a "ball" effect and improve the wrapping and workability, Due to the increase of cohesiveness, the anti segregation performance of concrete is greatly improved, and the aggregate is uniformly suspended in the cement paste, which reduces the friction between them in the flow process, so as to improve the fluidity, the friction between the aggregate and the aggregate, and increase the slump and expansion. The viscosity of hpmc-3w is small, and the second factor is dominant at low content, so the slump increases. With the increase of the content, the first factor dominates, so the slump and expansion decrease; the viscosity of hpmc-10w is medium, and the effect of the two factors under the action of low content is offset, the slump remains unchanged, the first factor dominates when the content is increased, and the slump and expansion decrease; The viscosity of hpmc-20w is high, and the first factor is dominant under different dosage, so the slump and expansion of hpmc-20w are higher.
2.2 effect of cellulose ether on compressive strength (see Fig. 3-4)
Fig. 3 Influence of HPMC on compressive strength of concrete at 3d age
Fig. 4 Influence of HPMC on compressive strength of concrete at 28d age
The influence of HPM on the compressive strength of concrete is shown in Fig. 3 ~ 4. HPMC is a kind of high molecular polymer, which can bond Ca (OH) 2 to increase the cohesive force of cement paste. At the same time, due to the effect of increasing viscosity and water retention, it reduces the micro cracks of concrete in the process of hardening, so as to improve the strength of concrete. These two effects jointly affect the compressive strength of concrete. It can be seen from Fig. 3 that for HPMC with three viscosities, the first one plays a leading role in low content, which improves the early compressive strength of concrete, and reaches the maximum value at 0.0025%. Then, with the increase of the content, the second function plays a leading role, and the compressive strength decreases. As can be seen from Figure 4, the same is true for hpmc-3w and hpmc-10w.The compressive strength of hpmc-20w concrete decreases with the increase of the content. For hpmc-20w, the later compressive strength decreases with the increase of the content. According to figures 3-4, for HPMC, the higher the viscosity, the lower the strength of concrete with the same content.
2.3 effect of cellulose ether on water retention (see Figure 5)
Figure 5 shows the influence of HPMC on the water retention of concrete. HPMC with three viscosities can reduce the water loss of concrete and improve the water retention. Under the same dosage, the higher the viscosity of HPMC, the better the water retention effect of concrete. The slope of the three curves shows the difference of the influence of different viscosity HPMC dosage on water retention. The viscosity of hpmc-3w is the smallest. When the dosage is less than 0.0050%, the increase of water retention effect is small. When the dosage is greater than 0.0050%, the unit dosage and water retention efficiency will be improved. The viscosity of hpmc-10w is in the middle, and the water retention is proportional to the content, and gradually increases with the increase of the content. The viscosity of hpmc-20w is the highest, the increase of water retention effect is larger when the content is less than 0.0050%, and the increase of water retention effect is smaller when the mixing amount is greater than 0.0050%.
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