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This study aims to evaluate the physical properties of non-sintering cement (NSC) concrete by adding phosphogypsum (PG) and waste lime (WL) to granulated blast furnace slag (GBFS) as sulfate and alkali activators. The study measured changes in the physical properties of fresh concrete using NSC, and the compressive, flexural and tensile strength of the hardened concrete for 360 days. In the results of the experiment, concrete using NSC was superior to that using Ordinary Portland Cement (OPC) or blast-furnace slag cement (BSC) in terms of fluidity and hydration heat characteristics. In addition, the early strength of concrete using NSC was relatively low at around 85% of the strength of concrete using OPC on day 3, but this was reversed from day 7 and the difference between OPC and BSC grew steadily larger over time until day 360. The strength of concrete using NSC develops continuously because the GBFS component eluting as GBFS is activated by PG and WL, and due to their reaction, ettringite, C-S-H gel, etc. are generated steadily for a long time, and there is no transition zone in the interface between the aggregate and paste because Ca (OH) is hardly generated from the hydration process, and as a result, interfacial adhesion is reinforced with aging. Keywords: granulated blast-furnace slag; phosphogypsum; waste lime; waste management; hydration 1. Introduction granulated blast furnace slag (GBFS) as sulfate and Greenhouse gas reduction will be highlighted as alkali activators. the most pending question in the cement industry in In order to examine changes in the physical future because the production of Portland cement not properties of fresh concrete using NSC, authors only consumes limestone, clay, coal, and electricity, measured slump, air content, bleeding, and hydration but also releases waste gases such as CO , SO , and heat. In addition, the strength characteristics of 2 3 NO , which can contribute to the greenhouse effect hardened concrete were examined by measuring the and acid rain. GBFS is a byproduct generated from compressive, flexural, and tensile strength from 3 the iron manufacturing process. It does not become to 360-days and analyzing the internal microscopic hydrated upon contact with water, but tends to be structure. This study also investigates the basic hydrated and hardened when adding activators, such physical properties and quality of concrete using 1), 2) as alkali or sulfate . In Korea, 30 million tons of PG NSC, and evaluates the possibility of reusing it as a and 3 million tons of WL have been accumulating as construction material. 3) wastes , and their disposal has become a serious social 4) issue . 2. Experiment This study aims to evaluate the physical properties 2.1 Raw Materials for Binder Systems Samples of non-sintering cement (NSC) concrete by adding The blast furnace slag used was obtained from a phosphogypsum (PG) and waste lime (WL) to K steel plant in Korea. The PG used for the sulfate activator was obtained from a phosphoric acid factory (N-Chemical) as a filter cake. The waste lime used *Contact Author: Wongil Hyung, Professor, for the alkali activator was obtained from a sodium School of Architecture, Yeungnam University, carbonate (Na CO ) factory (D-Chemical) as a filter 2 3 Dae-dong, Gyeongsan, 712-749, Korea cake. Also, a small quantity of commercial slacked lime Tel: +82-53-810-2597 Fax: +82-53-810-4625 (SL) was applied as an alkali activator. BFS was ground E-mail: firstname.lastname@example.org in a laboratory ball mill and the material passed through ( Received April 7, 2014 ; accepted November 14, 2014 ) a 30-micron sieve was used in the preparation of cement Journal of Asian Architecture and Building Engineering/January 2015/195 189 Table 1. Chemical Composition and Physical Properties of Raw Materials Item Oxide composition (%) Blaine Specific Type (g/cm ) gravity SiO Al O CaO Fe O MgO Na O K O P O TiO SO LOI 2 2 3 2 3 2 2 2 5 2 3 GBFS 34.76 14.50 41.71 0.48 6.87 0.14 0.44 0.03 0.62 0.13 0.23 4,600 2.91 APG 1.34 0.12 40.97 0.04 - 0.06 - 0.64 0.05 54.93 0.81 4,300 2.88 DPG 1.08 0.07 32.28 0.21 0.05 - - 0.58 0.04 43.29 22.37 4,100 2.36 SL - 0.19 65.88 0.12 1.03 - - - 0.03 1.13 31.51 5,400 2.27 WL 4.88 1.62 42.12 1.35 6.89 0.11 1.89 0.02 0.02 3.12 33.17 4,100 2.22 OPC 20.88 5.39 64.73 2.38 1.51 0.27 0.22 - 1.33 1.65 2.04 3,300 3.15 Table 2. Mix Proportions of Concrete Using Various NSCs Mixing proportion Air entraining and Type Mix proportions of NSC (wt%) Gmax W/C S/a W (kg/m ) water reducing (mm) (%) (%) (kg/m ) agent OPC GBFS AG DG SL WL C S G OPC 100 - - - - - BSC 50 50 - - - - NSC1 - 87 12 - 1 - NSC2 - 87 6 6 1 - 20 45 41 179 397 736 1060 C× 0.5% NSC3 - 82 - 17 1 - NSC4 - 85 11 - - 4 NSC5 - 81 11 - - 8 samples. The blain's surface areas of GBFS were 4,600 strength characteristics of concrete, authors prepared cm /g. The glass content of the GBFS, was 99.8% as specimens according to KS F 2405, placed them in determined by the optical microscopic method. PG Ø10×20cm and 15×1, 5×55cm molds, cured them in was prepared by washing with 0.5% milk of lime at a standard curing room (20°C, 50% RH) for a day, 20°C for 5 min. The PG/milk of lime ratio was 14% cured them in water at 20± 2°C, and then measured the by weight. After neutralization treatment, the PG was compressive, flexural and tensile strength at the age of 3, dried at 80°C in order to obtain dehydrate gypsum 7, 28, 90, and 360-days. (CaSO • 2H O, DPG) and was calcined at 450°C in 4 2 order to obtain anhydrite (II-CaSO , APG). Then, the 3. Results and Discussion 5), 6) DPG and APG were refined by refiner machine . 3.1 Slump and Air Content of Fresh Concrete Waste lime was dried at 90°C for 1-day and refined by Fig.1. shows the results of experiments on slump a refiner machine. OPC and blast-furnace slag cement and air content according to cement type. In terms of (BSC) were applied in order to compare their physical fluidity, NSC concrete was generally superior to OPC properties with that of NSC. Their chemical and or BSC concrete except NSC 4 and 5, which used WL. physical properties are shown in Table 1. Crushed stone This was due to the fact that the surface of GBFS is 20mm (specific gravity = 2.60g/cm , F.M. = 6.68) was of a smooth wave form, and the interface lubrication used as coarse aggregate, and river sand was used as effect of acidic film formed on the surface increases 6), 7), 8) fine aggregate for the physical concrete test. AE water- lubrication among the particles of fresh concrete . reducing admixture of naphthalene type was used to As to the fluidity of concrete according to the type of secure the fluidity and air content . activator, in the case of PG used as a sulfate activator, 2.2 Mixture Proportion and Experimental Method fluidity was not affected much by whether anhydrite The NSC mixtures were prepared by mixing or hydrate gypsum were used, but fluidity showed the different proportions of GBFS, PG, WL and SL. Table tendency of decreasing with the increase in the content 2. shows the mix proportion of concrete using various of WL and the decrease in the content of GBFS. In the NSCs. In an experiment with fresh concrete, slump, air results of an experiment on air content, NSC showed content, and bleeding tests were performed according the tendency of decreasing compared to OPC and BSC to KS F 2402, 2421 and 2414, respectively. In order to and this was due to the fact that the GBFS used in the measure hydration reaction heat according to the age experiment has a higher fineness (4,600 cm /g) than of concrete by cement type, authors prepared a 64ℓ OPC and its content is 81~87%, almost 2 times higher (40×40×50cm) mold insulated with insulation material, than that of BSC, and thus the inter-particle filling placed concrete just after mixing, and measured the effect is enhanced by the fineness. As to the air content change of temperature inside the concrete by setting of NSC according to the activator type, the air content a thermocouple at the core of the concrete and using decreased markedly in NSC 4 and 5 containing WL as a data logger (TDS-602). In order to compare the an alkali activator. 190 JAABE vol.14 no.1 January 2015 Seongjin Yoon Fig.2. shows the slump loss of concrete over time. as well, bleeding capacity did not decrease notably Slump loss was significantly less in concrete using because the overall adsorption of water was not much, NSC than in OPC, and also less than in BSC. This was and in the case of NSC3 added in the form of DPG, due to the content of GBFS, whose surface adsorption bleeding capacity was much higher than that of NSC1 of dispersant is lower than OPC, which was high. that used only APG. In the case of NSC 4 and 5 that That is, the setting time was lengthened by admixture used WL, however, bleeding capacity decreased and cement not being adsorbed into the surface of the considerably as WL adsorbed water. dispersant and by redundant water not being involved in the early hydration reaction. A low rate of slump 0.35 OPC decrease means that the security of workability lasts BSC 0.30 for a longer time. NSC1 NSC2 0.25 NSC3 20 8 NSC4 Air Content(%) NSC5 0.20 Slump(cm) 0.15 15 6 0.10 0.05 10 4 0.00 0 50 100 150 200 250 Time (min) F i g . 3 . B l e e d i n g Capacity of Fresh Concrete Over Time 0 0 According to Cement Type OPC BSC NSC1 NSC2 NSC3 NSC4 NSC5 Type of Cement 3.3 Hydration Temperature During Setting and Fig.1. Slump and Air Content of Fresh Concretes with Hardening Various Cement Types Fig.4. shows the temperature of specimens in a simple adiabatic temperature test for OPC, BSC and NSC1. Peak temperature was high in the order of OPC>BSC>NSC1, and the time to reach the peak temperature was long in the reverse order. Peak temperature was 60°C in concrete using OPC, 52.7°C in BSC, and 48.9°C in NSC1. The time to reach the peak temperature in the core was 14 hours in OPC, OPC BSC 22 hours in BSC, and 27 hours in NSC1. That is, NSC1 peak temperature decreased and the time to reach the NSC2 NSC3 peak temperature increased with the decrease in the NSC4 OPC content. The rise of concrete temperature by the NSC5 hydration heat of cement in the process of concrete 0 hardening affects the properties of the concrete 0 20 40 60 80 100 120 including strength development. Particularly in the Time (min) case of high-strength concrete with a large unit volume of cement and mass concrete with difficulty in the Fig.2. S l u m p L o s s o f Concrete Over Time According to emission of internal temperature, it is not easy to have Cement Type cracks or the lowering of strength due to temperature 3.2 Bleeding of Fresh Concrete stress resulting from the temperature difference Fig.3. shows the bleeding capacity of fresh concrete between the inside and outside of the concrete. Thus, over time according to cement type. In general, it is considered very effective if NSC is used as a bleeding capacity decreases with the increase in substitute for OPC and BSC in order to lower hydration fineness, but in authors experiment, the bleeding heat because NSC does not contain clinker in OPC. capacity of BSC and NSC concrete was somewhat Fig.5. compared hydration heat characteristic higher than that of OPC. This is probably because according to the mixture of NSC cement. Hydration when the content of GBFS is high the fluidity of heat was highest in NSC1 using APG, and decreased concrete increases and there exists some redundant by 3.1°C in NSC2 using some DPG together with APG water and the low activity of GBFS delays early compared to NSC1 and decreased by 3.9°C in NSC3 3) hydration reaction to some degree . In the case of PG using DPG only. This was due to the fact that the JAABE vol.14 no.1 January 2015 Seongjin Yoon 191 Slump (cm) Slump loss (%) Air content (%) 3 2 Bleeding capacity (cm /cm ) hydration heat of APG is higher than that of DPG. The steadily. Particularly from day 28, concrete using OPC time to reach the peak temperature was around 3 hours showed a slowdown in the increase of strength but shorter in NSC2 than in NSC1, but around 7 hours NSC concrete showed the tendency of steady increase longer in NSC3 than in NSC1. In the case of NSC4 and of strength in an almost linear form until day 360. NSC5 using WL, the temperature was higher than that Furthermore, NSC1 had a higher strength than BSC at of NSC1 for the first 16 hours of hydration and then the early age. The strength of NSC2, the concrete of went down gradually, and their peak temperature was cement mixture in which 50% of APG was replaced lowest while their time to reach the peak temperature with DPG, was lower than that of concrete using only was long. This was due to the fact that the elution rate APG on day 3, but was almost equal at the age of and activation of WL are very slow. These results show 7~360-days. The strength of NSC3, the concrete of that the hydration heat of NSC is very low and the cement mixture using DPG as an activator instead of use of DPG or WL as an activator is quite effective in APG, was around 75% of the mixture of NSC1 on day reducing hydration heat further. 3, but around 80% on day 7 and almost equal from day 28. Because the elution of APG, a soluble substance, is around 2 times larger than DPG, there are more OPC opportunities to contact acidic film on the surface of a BSC NSC1 GBFS particle, and because APG has higher hydration Open air heat emitted during elution than DPG, the use of APG increases early strength but, over time, its effect weakens gradually and in the end it becomes similar to 6), 7) that with the use of DPG . In the case of NSC4 and NSC5 containing WL, strength during the first three days is quite low at around 70~75% of that of NSC1, but their compressive 25 strength on day 7 and day 28 is almost identical with that of NSC2. In particular, NSC5 shows the highest strength at the age of 90 days and afterward. This 0 10 20 30 40 50 60 70 was due to the fact that the alkali activation of WL is Time (hour) weaker than that of SL but it continuously maintains an atmosphere of over pH12 and, after all, destroys the Fig.4. Temperature of Specimens in a Simple Adiabatic acidic film of GBFS. It is believed that there is high Temperature Test for OPC, BSC and NSC1 improvement in strength at a long age because hydrate 65 is generated from hydration reaction between modified NSC1 ion and PG inside GBFS, and substances other NSC2 than calcium hydroxide inside WL such as calcium NSC3 NSC4 carbonate and other inorganic materials behave stably NSC5 while playing the role of filler without hindering Open air 40 80 OPC BSC NSC1 NSC2 NSC3 NSC4 NSC5 0 10 20 30 40 50 60 70 Time (hour) Fig.5. Hydration Temperature Compared Hydration Heat Characteristic According to the Mixture of NSC Cement 3.4 Strength Fig.6. shows the results of an experiment on concrete strength according to cement type. In general, compressive, flexural, and tensile strength show 0.0 similar tendencies according to age. NSC concrete was 3 7 28 90 360 less strong than OPC at the age of 3-days but it was Curing Age (days) reversed from day 7 and the difference grew larger with aging as the strength of NSC concrete increased a) Compressive strength 192 JAABE vol.14 no.1 January 2015 Seongjin Yoon o o Temperature ( C) Temperature ( C) Compressive Strength (MPa) 3.5 Distribution of Transition Zone Inside Concrete OPC BSC NSC1 NSC2 NSC3 (a) OPC (b) BSC NSC4 2 NSC5 3 7 28 90 360 Curing Age (days) (b) Flexural strength (c) NSC Fig.7. SEM Analysis of Aggregate Interface Inside Concrete Using OPC, BSC and NSC at the Age of 90 Days Fig.7. shows the result of SEM analysis of aggregate OPC interface inside concrete using OPC, BSC and NSC BSC at the age of 90 days. The discontinuous area existing NSC1 between aggregate and paste is called a transition zone, NSC2 and is formed mainly by Ca (OH) crystal (within NSC3 2 NSC4 75 m). In the case of OPC, Ca (OH) eluted on the NSC5 surface of aggregate is around 25 m thick, and as 1 μ the transition zone does not have an adhesive force, if it receives pressure, cracks occur and spread by the concentration of stress. Therefore, the quantitative 3 7 28 90 360 change in the transition zone has a significant effect on Curing Age (days) compressive strength. In the case of BSC, Ca (OH) generated from OPC is consumed mostly through (c) Tensile strength hydration reaction with GBFS, and therefore, the Fig.6. Strength of Concretes with Various Cement Types width and volume of the transition zone decreases considerably compared to that in OPC. Furthermore, the hydration reaction. Accordingly, it is considered NSC cement generates little Ca (OH) in the hydration possible to reduce the input of GBFS and manufacture process, so it does not have a transition zone in the superior cement of high economic efficiency using interface between aggregate and paste and, as a result, WL, an industrial waste, as an alkali activator along the adhesive force and compressive strength increase with DPG in manufacturing secondary products of 12), 13), 14) over time . concrete without considering early strength. Compared 3.6 Pore Size Distribution and Pore Volume to OPC and BSC, NSC can develop higher strength Figs.8. and 9. show, respectively, the ratios of at a long age because by the activation effect of PG flexural and tensile strength to compressive strength in and WL, the elution of GBFS components and their NSC concrete. Different from those in OPC and BSC, reaction generates ettringite, C-S-H gel, etc. steadily the ratios of flexural and tensile strength to compressive 8), 9), 10), 11) even at a long age . As a result, the maximum strength in NSC concrete vary slightly according to compressive strength of a 1-year-old specimen of NSC age. The flexural strength of OPC and BSC concrete is concrete is around 1.5 times higher than that of OPC around 15~17% of compressive strength, and increases and around 1.25 times higher than that of BSC. gradually or remains almost constant over time. In contrast, the flexural strength of NSC concrete is JAABE vol.14 no.1 January 2015 Seongjin Yoon 193 Tensile Strength (MPa) Flexural Strength (MPa) around 15~20%, slightly higher than that of OPC and of 7-days than at other ages in NSC concrete may be BSC and, in particular, flexural strength at the age of 7 that the production of ettringite, a needle-like crystal days is around 18~20% of compressive strength, higher substance, reaches its peak at the age of 7-days and the than that at other ages. The tensile strength of OPC substance plays the role of a fine short staple and form and BSC concrete is around 7.5~9% of compressive network structure inside the hardened concrete. strength, and is almost constant regardless of age. The tensile strength of NSC is 7.5~10% of compressive 4. Conclusion strength, slightly higher than that of OPC and BSC. As a measure to save resources and energy and reuse Its tensile strength at the age of 7-days is 9~10% of industrial byproducts in the cement industry, this study compressive strength, higher than that at other ages. evaluated the basic properties of concrete using NSC. The reason why the ratios of flexural and compressive The results are as follows: strength to compressive strength are higher at the age 1. As to the characteristics of fresh concrete, NSC was superior to OPC or BSC in fluidity and hydration heat, OPC but not in air content and bleeding capacity. BSC 2. Though the strength of concrete using NSC is low NSC1 during the initial 3-days, it shows equal or higher NSC2 strength development compared to OPC or BSC after NSC3 7-days and onwards. NSC4 NSC5 3. Owing to continuous reactions of GBFS, PG and WL during the long-term strength development of NSC concrete, ettringite and C-S-H gel are generated even in long age, and little Ca (OH) is generated during concrete hydration. This might be because as a result, transition zones are not created in the interfaces of aggregate and paste, causing excellent adhensivity to interfaces. 4. Should strength at the early stage not be considered as an important factor, use of waste gypsum and waste lime landfill with simple preconditioning process reduces the volume of furnace slag powder to be used and so enables manufacturers to produce NSC with 3 7 28 90 360 economic merits. Curing Age (days) Acknowledgment Fig.8. Flexural Strength/Compressive Strength Ratio This w ork was supported by the National o f C o n c r e t e s with Various Cement Types Research Foundation of Korea Grant funded by the Korean Government (MSIP) (2014, Joint Research Corporations Support Program). References 1) K. J. 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Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: Jan 1, 2015
Keywords: granulated blast-furnace slag; phosphogypsum; waste lime; waste management; hydration
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