Hydration and Hardness Features of Green Concrete

Transcription

1 Hydration and Hardness Features of Green Concrete Sun Wen-biao Department of Safety Engineering Henan Institute of Engineering Zhengzhou, China ABSTRACT Green cement that contained about 7 percent of slag and fly ash was prepared. With the green cement used as cementitious material, green concrete was made. Compressive strength and bending strength of the green concrete was tested with standard ways. The interfacial transition zone (ITZ) in the green concrete was observed with SEM. The results showed that both the compressive strength and the bending strength of the green concrete were higher than those of ordinary concrete. The ITZ in the green concrete was more compact than that in ordinary concrete. The higher strength of the green concrete is due to the more compact ITZ in it and the more compact ITZ in green concrete results from the dissolving and welding action of rock formation agent. KEYWORDS: green cement; green concrete; strength; ITZ INTRODUCTION Concrete is one of the most widely used building materials in the world. Traditional Portland cement not only consumes a large amount of resource and energy, but also causes serious environment pollutions during the course of manufacture. Green concrete is one of the developments of modern concrete [1-3]. Adding industrial wastes to cement or concrete is one of ways to transform ordinary concrete to green concrete. Cement that contains much industrial wastes has been studied in recent years. Many conclusions indicated that if industrial wastes take the place of clinker, the early strength of the cement will decrease. The authors prepared green cement that contained a big part of slag and fly ash, as particular additives were added in, the green cement did not have lower strength than that of traditional ordinary cement. This article researches the strength of green concrete with the green cement was used as cementitious material. As the interfacial transition zone (ITZ) between the cementitious materials and the aggregates has important implications on properties of concrete, the ITZ in green concrete is observed by Scanning Electron Microscopy (SEM) in order to explain the advantage of green concrete

2 Vol. 22 [217], Bund RAW MATERIALS AND DESIGN OF EXPERIMENT Raw materials The green cement that contained about 7 percent of slag and fly ash was used as cementitious material. Some additives were added to the green cement to promote hydration of the slag and the fly ash. 32.5# and 42.5# ordinary Portland cement that produced in Hebei Province was used as standard sample. The middle sand with fineness modulus of 2.7 was used as fine aggregate in concrete. Broken stones with diameter of 5~25 mm was used as coarse aggregate. The mixing water is ordinary tap water. Design of experiment Hydration and hardness characteristics of concrete conclude macro-indicators such as compressive strength and micro structure such as the interfacial transition zones (ITZ). In order to study the strength of green concrete systematically, three strength grades (c3, c4 and c5) of concrete was designed as shown in Table1. Concrete with green cement used as cementitious material is green concrete, while ordinary Portland cement makes ordinary concrete. Table 1: Mixture ratio of concrete number cementitious material C S G W UNF-5 C3-1 green cement 42.5# C3-2 ordinary Portland cement # C4-1 green cement 32.5# C4-2 ordinary Portland cement # C5-1 green cement 42.5# C5-2 ordinary Portland cement 42.5# C S G W and stand for cementitious material, sand, stone, water and superplasticizer respectively. In order to observe the structure of ITZ, two kinds of cement mortar were made, the aggregates in cement mortar are small limestone particles. Both kinds of cement mortar were treated for 28 days and sawn to reveal fresh smooth surface.

3 Vol. 22 [217], Bund RESULT OF EXPERIMENT AND DISCUSSION Compressive strength Compressive strength of green concrete and ordinary concrete is shown in Figure 1to Figure 3. 6 Compressive strength/mpa C3-1 C3-2 Figure 1: Compressive strength of C3 green concrete and ordinary concrete Compressive strength/mpa C4-1 C4-2 Figure 2: Compressive strength of C4 green concrete and ordinary concrete

4 Vol. 22 [217], Bund Compressive strength/mpa C5-1 C5-2 Figure 3: Compressive strength of C5 green concrete and ordinary concrete Figure 1 through Figure 3 indicate that all compressive strength of concrete increases with the increasing of age. When the mixture ratios and ages are comparable, green concrete has far higher compressive strength than that of ordinary concrete. Bending strength Bending strength of green concrete and ordinary concrete is shown in Figure 4 to Figure 6. Bending strength/mpa C3-1 C3-2 Figure 4: Bending strength of C3 green concrete and ordinary concrete

5 Vol. 22 [217], Bund Bending strength/mpa C4-1 C4-2 Figure 5: Bending strength of C4 green concrete and ordinary concrete 8 7 Bending strength/mpa C5-1 C5-2 Figure 6: Bending strength of C5 green concrete and ordinary concrete Figure 4 through Figure 6 indicate that all bending strength of concrete increases with the increasing of age. When the mixture ratios and ages are comparable, green concrete has higher bending strength than that of ordinary concrete. Structure of ITZ Topography of ITZ in green concrete and ordinary concrete are shown in Figure 7 and Figure 8 in which the upper parts are cement paste and the lower parts are limestone particles.

6 Vol. 22 [217], Bund Figure 7: Interfacial transition zone in green concrete Figure 8: Interfacial transition zone in ordinary concrete

7 Vol. 22 [217], Bund Figure 7 and Figure 8 show that the ITZ in green concrete is more compact than that in ordinary concrete. There is a narrow gap in the ITZ in ordinary concrete. The gap should be filled with water in realistic concrete. The cause of difference in ITZs relates to the solution and welding action of rock formation agent in green cement. In order to prove this opinion, the solution experiment of rock formation agent to limestone powders is conducted. The dissolving time is 24 hours. The morphologies of the powders before and after solution are shown in Figure 9. A Raw limestone powder Figure 9: Continues on the next page

8 Vol. 22 [217], Bund B limestone powder dissolved by ordinary cement solution C limestone powder dissolved by green cement solution Figure 9: Morphologies of limestone powders before and after solution

9 Vol. 22 [217], Bund Morphologies of A and B in Figure 9 are almost the same as each other, while morphology of A and C are obviously different from each other. Rock formation agent in green cement dissolves and welds the aggregate so as to make the structure of ITZ compact. Compact structure of ITZ contributes to high strength of green concrete. CONCLUSION AND PROSPECT (1) The compressive strength and bending strength of green concrete is higher than that of ordinary concrete. (2) The ITZ in green concrete is more compact than that in ordinary concrete, which is due to the dissolving and welding action of rock formation agent in green cement. (3) The other characteristics of green concrete are still to be studied. REFERENCES [1] Wang Zhao, Yang Rui. Research and exploration of green high performance concrete [J]. Concrete, 21 (4), pp.1-13 (in Chinese). [2] Liu Cui-lan, Zhang Feng-chen, Chen Yongjun. Investigation of modification of ordinary concrete to GHPC [J]. Journal of Lanzhou University of technology, 26,32 (3), pp (in Chinese). [3] Wang Zhen-jun, Chen Ping, Shang Ji-ge. Research progress on durability of green high performance concrete [J].Concrete, 29 (11), pp (in Chinese). [4] Zeng Li, Ge Xueliang. Hydration property of phosphorous-slag in complex binding material [J].Engineering Journal of Wuhan University, 21,43(3), pp (in Chinese) [5] Dong Liang. Application of mineral admixtures in high performance concrete [J]. Journal of railway science and engineering, 21,7(2), pp.58-6 (in Chinese). 217 ejge Editor s note. This paper may be referred to, in other articles, as: Sun Wen-biao: Hydration and Hardness Features of Green Concrete Electronic Journal of Geotechnical Engineering, 217 (22.15), pp Available at ejge.com.

10 Vol. 22 [217], Bund About the author SUN Wen-biao, male, Associate Professor. Department of Safety Engineering, Henan Institute of Engineering, Zhengzhou , China; Tel: