Table 1. Density and absorption capacity of Chinese and Japanese lightweight aggregates

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1 RESEARCH WORK 1. Objective The objective of this research is to determine the influence of Interfacial Transition Zone (ITZ) around Lightweight aggregate in concrete on Chloride ion diffusivity. 2. Introduction The ITZ of conventional concretes is the weakest point of concrete. The accumulating water on ITZ zone forms the most permeable area inside the concrete. Hence ITZ paves the way for chloride ion diffusion. The quality of ITZ depends on type and quality of aggregates used, water-cement ratio and also the method used for the production of concrete. In this research two types of lightweight aggregates will be used. One of them is Chinese lightweight aggregate having low absorption capacity and the other, is Japanese lightweight aggregate with high absorption capacity. The idea is to produce concrete with same effective water - cement ratio, using the same aggregates in two different conditions, dry and saturated, and compare the chloride ion diffusivity in these concretes (by diffusion test). A comparison of ITZ thickness of these concretes by SEM and EDAX-maps is also proposed. The chloride ion diffusion of concretes produced with the same effective water - cement ratio and same aggregates (dry and ssd) will depend, mainly, on ITZ. 3. Experimental Phase 3.1 Properties of aggregates Chinese and Japanese lightweight aggregates are used for concrete production. The Silica is the main composition of them. The physical properties (density and absorption capacity at 1 minutes, 1 hours, 6 hours and 24 hours) of these aggregates are determined as shown in table 1. The pictures of Chinese and Japanese aggregates are shown in figure 1.. Table 1. Density and absorption capacity of Chinese and Japanese lightweight aggregates Lightweight Density (kg/dm 3 ) Absorption (%) aggregates Dry SSD 1 min 1 hour 6 hours 24 hours Chinese Japanese

2 a) b) Figure 1. Shape of lightweight aggregates. a) Chinese lightweight aggregates b) Japanese lightweight aggregates 3.2 Concrete production Two types of concrete are produced using Ordinary Portland Cement, natural fine aggregates and lightweight coarse aggregates. Type I Two concrete samples are made with Chinese lightweight aggregates with effective water-cement ratio.4. They are designated as CLDRY.4 (aggregates dry) and CLSSD.4 (aggregates ssd). When the aggregates are in dry condition, 1hr absorption capacity (.58%) is considered. Type II Six concrete samples are made with Japanese lightweight aggregates with effective water-cement.4,.5 and.7 using dry aggregates and ssd aggregates. Dry aggregates with 1 hr absorption capacity (7.29%) is considered for concrete production. The samples are designated as JLDRY.4, JLSSD.4, JLDRY.5, JLSSD.5, JLDRY.7, JLSSD.7. Mix proportions of all concretes are illustrated in table 2 and some pictures of concrete production in fig. 2 2

3 Table 2. Concrete mix proportions for all type of concretes Fresh concrete Hard. concrete Mix proportions (kg/m 3 of concrete) Slump (cm) Den. kg/m 3 Den. kg/m 3 Compr. Strength 28days Eff. w/c C W F.A C.A. dry C.A. s.s.d. W.R AE MPa CLSSD CLDRY JLSSD JLDRY JLSSD JLDRY JLSSD JLDRY Figure 2. Concrete production. The test elements of 2mm of length and 1 mm of diameter 3.3 Chloride ion diffusion in Hardened concrete The specimens were prepared according to the test method for effective diffusion coefficient of chloride ions in concrete by migration according to JSCE-G specification as shown in figure 3.. The specimens of each hardened concrete were tested at 3, 7 and 28 day of curing. 3

4 Figure 3. Test method for effective diffusion coefficient of chloride ions in concrete by migration according to JSCE-G Figure 4, 5 and 6 show the results of the accelerated chloride diffusion test with an electrical potential of 15 volts of all concretes at 3, 7 and 28 curing days respectively. The increase of chloride ions in the inside NaOH solution with time is shown..35 Chloride ions (m ol/l) JL.SSD -.7 JL.D RY-.7 JL.SSD-.5 JL.D RY-.5 JL.SSD -.4 CL,SSD -.4 JL.D RY-.4 CL,D RY Days Figure 4. Accelerated chloride diffusion test for 3 days of curing 4

5 .35.3 JL.SSD-.7 Chloride Ion flux (m ol/l) JL.DRY-.7 JL.SSD-.5 JL.DRY-.5 JL.SSD-.4 JL.DRY-.4 CL.D RY-.4 CL.SSD Days Figure 5. Accelerated chloride diffusion test for 7 days of curing,35,3 Chloride ion flux (mol/l),25,2,15,1,5 JL-SSD-,7 JL-DRY-,7 JL-SSD-,5 JL-DRY-,5 JL-SSD-,4 JL-DRY-,4 CL-DRY-,4 CL-SSD-, Days Figure 6. Accelerated chloride diffusion test for 28 days of curing The rate of the increasing amount of chloride ions in the solution became constant with time. In the case of 3 days curing concretes, it became constant with time after about 4, 2 and 1 days in concretes made with.4,.5 and.7 effective water-cement ratio respectively. In the case of 7 days curing concretes the steady condition was attained after about 4 days, in concretes made with.4 effective water-cement ratio, after about 3 days in concrete made with.5 effective water-cement ratio and dry aggregates, and 5

6 after about 1 day in concrete made with.5 effective water-cement ratio and ssd aggregates and concretes made with.7 effective water-cement ratio. In the case of 28 days curing concretes the steady condition was attained after about 7 days in concretes made with.4 effective water-cement ratio except in the case of concrete made with Japanese lightweight aggregates which get at 3 days. Concrete made with.5 effective water-cemet ratio with aggregates in saturated and dry condition, the steady condition was got at 3 and 4 days respectively. After about 2 days in concrete made with.7 effective water cement ratio. A linear regression line was determined after the transition period. The slope is the flow rate of chloride ions for each concrete mix. The flux of chloride ions in steady state for each concrete at different period of curing are calculated according the equation 1 and the results are shown in table 3. Jcl= V/A* Ccl/ t [1] Where, Jcl: Flux of chloride ions in steady state (mol/(cm 2 *year)) V : Volume of anode solution (L) A: Cross section of specimen (cm 2 ) Ccl/ t: Rate of increase in chloride ion concentration on anode side ((mol/l)/year) Table 3. Flux of chloride ions in steady state for each concretes. Type of concrete Flux of chloride ions in steady state (mol/cm 2 * year)) 3 days curing 7 days curing 28 days curing CLSSD.4 8.5E E-5 4,915E-5 CLDRY E E-5 6,862E-5 JLSSD E E-5 5,837E-5 JLDRY E E-5 6,981E-5 JLSSD E E-5 1,874 E-5 JLDRY E E-5 12,363 E-5 JLSSD E E-5 13,279 E-5 JLDRY E E-5 12,821 E-5 These flux values were then used to calculate the diffusion coefficient of chloride ions using equation 2. The diffusion coefficients of each concrete of 3 days, 7 days and 28 days of curing are illustrated in figure 7. 6

7 De= (JclRTL)/( Zcl FCcl( E- Ec)*1 Where, De: Effective diffusion coefficient (cm 2 /year) R: Gas constant (= 8.31 J/(mol*K)) T: Absolute temperature (K) Zcl: Change of chloride ion (=-1) F: Faraday constant (= 965 C/mol) Ccl: Measured chloride ion concentration on cathode side (mol/l) E - Ec: Electrical potential difference between specimen surfaces (V) L: Length of specimen (mm) Effective diffusion coef. (cm2/sec x1-11) days curing SSD aggregates DRY aggregates CL-.4 JL-.4 JL-.5 JL-.7 Type of concrete Effective diffusion coef.(cm2/sec *1-11) days curing SSD aggregates DRY aggregates CL-.4 JL-.4 JL-.5 JL-.7 Type of concrete Effective diffusion coef. (cm2/sec*1-11) days curing SSD aggregates DRY aggregates CL-.4 JL-.4 JL-.5 JL-.7 Type of concrete Figure 7. Effective diffusion coefficient in each concrete. It is clear that the effective water-cement ratio influences chloride ions diffusion, physical properties of aggregates and the condition of aggregates (saturated or dry) at the time of production of concrete. The chloride ion diffusion of the concretes made with Japanese lightweight aggregates 7

8 increase around 2-15% when the aggregates are in saturated surface dry (ssd) condition with respect to that for concretes made with aggregates in dry condition and same effective water-cement ratio at early age concretes. This is due to the accumulation of water in ITZ when the aggregates are in ssd condition and is more evident when the effective water-cement ratio of the concrete is high (I have to confirm with 28 days curing concretes). However this behavior is not very clear in concretes with 28 days of curing. The effective diffusion is decreasing clearly but the aggregate situation (ssd or dry condition) is also decreasing. (This behavior will be verified with 56 days and 9 days curing concretes) 3.4 Analysis of ITZ by SEM and EDX The samples are analysed by Scanning Electronic microscope to determine the microstructure of the Interfacial Transition Zone and the composition of the ITZ was measure by EDX. Concrete made.4 and.5 effective water-cement ratio and Japanese lightweight aggregates after 7 days curing were analysed. The aggregates were saturated and dry condition in both cases. In the case of concrete made with.4 effective water cement ratio the thickness of the interface is similar (around 5µm) of concrete made with aggregates in saturated or dry However the calcium silica ratio in the interface when the aggregates are saturated are 5.7 and when the aggregates are dry the calcium silica ratio is 4.8. Concretes made with.5 effective water-cement ratio with saturated and dry lightweight aggregates are shown in figure 8 and 9 respectively. The water accumulation happens in the interfacial transition zone when the aggregates are saturated condition. The calcium-silica ratio is much higer in concretes produce by saturated aggregates. 8

9 Research work in Tokyo Institute of Technology by Miren Etxeberria Figure 8. JLSSD.5. The bond point between aggregates and cement paste. Measurement of Ca/Si ratio in different points aggregate Figure 9. JLDRY.5. The bond point between aggregates and cement paste. Measurement of Ca/Si ratio in different points. 9