CAPÍTULO IV. CONDICIONES PARTICULARES DE CADA CATEGORÍA DE SUELO NO
SUBSECCIÓN 1. SUELO NO URBANIZABLE DE ESPECIAL PROTECCIÓN DE EMBALSES Y CAUCES
The suitable initiator of the polycarboxylate superplasticizer is important for the copoly- merization. We chose three different kinds of initiators to synthesze polycarboxylate super- plasticizer, and then we analyzed them by GPC, shown in Fig. 1.
The curves of GPC were divided into three different areas by the GPC peaks. As shown in Fig. 1, the area of peak, at 15~23 min of elution time, marked as I, is polycarboxylate superplasticizer. The peak at 23~25 min was marked as II. The last peak at 25~28 min was the peak of unreacted isoamyl alcohol polyxyethylene ether, marked as III. The polymer- ization conversion rate could be shown by the relative of area III. The fluidity of cement paste with different polycarboxylate superplasticizer is listed in Table 3. As shown in Table 3, the polymerization conversion rate is strongly influenced by different initiators. For the polycarboxylate superplasticizer synthesized with initiator C, the relative area III is smallest. This is means that the highest of polymerization conversion rate was obtained with initiator C. So the initiator C suits the polymerization in this paper.
Fig. 1 –The GPC of polycarboxylate superplasticizer with
different initiators.
Table 3 – the result of GPC and the fluidity of cement paste of PCs at 333 K.
initiator Mn Mw Mw/Mn acreage of peak /% fluidity of cement paste(0 h), mm(in) fluidity of cement paste(0.5h), mm (in) I II III
A 17900 40700 2.27 52 7 31 - -
B 18800 40000 2.13 76 6 18 190 (7.48) - C 18600 37600 2.02 78 6 16 255 (10.04) 170 (6.69)
The influence of temperature
The temperature of copolymerization influences the free radical generation, so we synthesized three polycarboxylate superplasticizers at different temperature, other reacted conditions being the same, as shown in Fig. 2. and Table 4. To get better information on the influence of the temperature, the curve of GPCs were segmented in four areas. Area I, the elution time at 15~18 min, was the polycarboxylate superplasticizers with higher molecular weight. The smaller ones, elution time at 18~23 min, were marked as area II. Area III, elution time at 23~25 min, and area IV, elution time at 25~28 min, were character- istic of unreacted monomer. Area IV was the peak of isoamyl alcohol polyxyethylene ether. By increasing the temperature from 323 K to 333 K, the percentage of area II became larger, while the percentage of area III and IV decreased, indicating that the polymeriza- tion conversion rate was higher. By further increasing the temperature up to 343 K, the percentage of area I increased, but the percentage of area III and IV also raised. The free radical generated faster when temperature rise to 343 K, so the percentage of polycar- boxylate superplasticizers with higher molecular weight raised. The test of cement paste showed the higher molecular weight of polycarboxylate superplasticizers could decrease the fluidity. So, the best temperature of copolymerization was 333 K.
The influence of initiator dosage
We synthesized three polycarboxylate superplasticizers with dosage of different initiator, the other conditions being the same, as shown in Fig. 3 and Table 5. As shown in Fig. 3, when the initiator dosage raised from 1.0% to 1.4%, the percentage of area I increased, and the percentage of area II raised. The test of cement paste showed that the initiator dosage influenced the polymerization conversion rate, and the best initiator dosage was 1.2%.
Fig. 2 – The GPC of polycarboxylate superplasticizers
synthetised under different temperature.
Synthesis and Properties of High Solid-Content Polycarboxylate Superplasticizer 129
The fourier transform infrared transmission spectrum of polycarboxylate superplasticizers
The FTIR spectrum of polycarboxylate superplasticizers is shown in Fig. 4. It was illus- trated that polycarboxylate superplasticizers had stretching vibration band of C-H in 2885 cm-1 (7328 in-1). The peak near 3441 cm-1 (8740 in-1)is assigned to the stretching vibration
band of O-H, and the peak at 1100cm-1 (2794 in-1)is from C-O-C stretching in polyxyeth-
ylene ether. The absorption bands at 1363cm-1 (3462 in-1)is the characteristic absorption
peak of carboxyl group of –COONa.
Properties of Concrete with PCs
The slump of the concrete was determined according to the Chinese National Standard GB/T 50080-2002. The water consumption was measured and the water-reducing rate of PCs was calculated, as shown in Table 6.
The water-reducing rate of PC was 32.5%, little higher than LS, which was 31.5%. The slump of concrete test showed almost the same properties of concrete with LS and PC.
Table 4 – the result of GPC and the fluidity of cement paste of PCs with different temperature (initiator C)
Tempera-
ture, K Mn Mw Mw/Mn
acreage of peak /% fluidity of cement paste(0 h), mm (in) fluidity of cement paste(0.5 h), mm (in) I II III IV 323 18100 41600 2.29 25 55 6 14 230 (9.06) 150 (5.91) 333 18900 41300 2.18 21 64 5 10 275(10.83) 210 (8.27) 343 25600 61600 2.41 38 43 7 11 160 (6.30) --
Fig. 3 – The GPC of polycarboxylate superplasticizers
CONCLUSIONS
Based on the results of this experimental work, the following conclusions can be drawn: 1. The factors influencing on the synthetic process were investigated and the optimum conditions were obtained, i.e. the initiator was C, reaction temperature of polymerization was 333 K, the initiator dosage was 1.2%.
2. In GPC the peak areas are proportional to concentration. So GPC method was used to determine the conversion data of reaction mixtures.
3. Compared with traditional polycarboxylate superplasticizer LS, the high solid-content polycarboxylate superplasticizer showed the same properties of concrete.
AUTHOR BIOS
Yongwei Wang is a researcher at the Shandong Provincial Academy of Building
Research, Jinan, China. He received his BS from Chongqing Jianzhu University; MS from Chongqing University; and PhD from Chongqing University. His research interests include civil engineering materials and hydraulic structures.
Table 5 – the result of GPC and the fluidity of cement paste of PCs with different initiator dosage (initiator C, 333 K)
initiator
dosage /% Mn Mw Mw/Mn
acreage of peak /% fluidity of cement paste(0 h), mm (in) fluidity of cement paste(0.5 h), mm (in) I II III IV 1.0 20000 44800 2.24 26 58 5 11 245 (9.65) 140 (5.51) 1.2 18900 41300 2.18 21 64 5 10 275 (10.83) 210 (8.27) 1.4 18600 38900 2.09 19 63 6 12 280 (11.02) 160 (6.30)
Fig. 4 – The FTIR spectrum of polycarboxylate
superplasticizers.
Synthesis and Properties of High Solid-Content Polycarboxylate Superplasticizer 131
Liya Wang is a Research Engineer at the Shandong Provincial Academy of Building
Research, Jinan, China. He received his BS from Shandong University; MS from Shan- dong University. His research interests include surface and interface activity of cement- water dispersion with superplasticizers.
Yongsheng Liu is a researcher at the Shandong Provincial Academy of Building
Research, Jinan, China. He received his BS from Shandong University; MS from Shan- dong University. His research interests include the synthesis of superplasticizers.
Zepeng Chu is a researcher at the Shandong Provincial Academy of Building Research,
Jinan, China. His research interests include the synthesis of superplasticizers.
REFERENCES
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3. Baskoca, A.; Ozkul, M. H.; and Artirma, S., “Effect of Chemical Admixtures on Work- ability and Strength Properties of Prolonged Agitated Concrete,” Cement and Concrete
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Table 6 – Water-reducing rate and slump of the concrete
Polymer water-reducing rate [%] slump of fresh concrete, mm (in) slump after1h, mm (in)
LS 31.5 80 (3.15) 60 (2.36)
One of the essential problems of superplasticized concrete is the loss of fluidity over time. To limit this problem one must improve the compatibility of superplasticizers and cement. This is not a trivial task as cement contains phases with different responses to superplasti- cizers in the first hours of hydration.
In the present work, the role of the polymer structure on the flow loss over time on superplasticized cement pastes has been studied. For this, we have correlated the impact of different molecular structures on the adsorption degree and ionic solution composition with the rheological properties of fresh cement pastes. The results revealed a high excess of aluminium in the aqueous solution. This could be due to aluminum complexation by the polymer or a poisoning of ettringite growth complemented by a stabilization of nano-sized ettringite particles. In addition, except for one of the studied polymers, the flow loss seems to decrease abruptly when the concentration of carboxylate ions in solution drops below a critical value (0.7-1.2 μeq/g).
INTRODUCTION
One of the essential problems of superplasticized concrete is the loss of fluidity over time.1 Consequently, flow loss can lead to water being added on job sites in order to recover
enough workability to place concrete. This compromises both strength and durability. To avoid such problems one must improve the compatibility of superplasticizers and cement. This is not a trivial task as cement contains phases with different responses to superplasti- cizers in the first hours of hydration.
The aluminates (C3A, 5-10% of the clinker mass) are the most reactive part of the clinker.
Both the adsorption of the PCEs on the surface of the hydrates (monoaluminatesulfate, AFm, and ettringite, AFt) and a complex intercalation of the polymer into the layers of the hydrates, forming new organo-aluminate composites, reduce the dispersing capability of the polymer.2-5 It is expected that this can be translated in a change of the specific
surface that probably affects the evolution of the flow. These perturbing phenomena can be handled to some extent by varying the admixture dosage to reach the initially desired flow. However, the evolution after that is much more problematic to manage.