D DAVID PUBLISHING. Damaging Formula of the Frost Resistant Concrete with Poor Quality of Coarse Limestone Aggregate. 1.

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1 Journal of Civil Engineering and Architecture 9 (2015) doi: / / D DAVID PUBLISHING Damaging Formula of the Frost Resistant Concrete with Poor Quality of Coarse Eneli Liisma and Lembi-Merike Raado Department of Building Production, Tallinn University of Technology, Tallinn 19086, Estonia Abstract: In this paper, concrete with limestone coarse aggregate was studied due to frost action in saline and nonsaline environments. The main focus is to explain the damaging formula of concrete with poor quality of limestone aggregate in frost actions. All investigated concretes fulfill the recommendations of the European standard EN 206, Concrete Specification, Performance, Production and Conformity limiting values for composition and properties of concrete (maximum W/C (water/cement) ratio, minimal class of compressive strength, minimal mass of cement and minimal percentage of entrained air). The damaging formula of the frost resistant concrete is studied through scaling test of concrete during freeze/thaw process, frost resistant test of coarse limestone aggregate and chemical analysis of limestone. Experiments results showed that there is a correlation between CaO/MgO ratio and Al 2 O 3 of limestone and frost resistance of concrete, using chemical composition for determining potential ACR (alkali-carbonate reactivity) will indicate higher risk of damaging effect of concrete. Key words: Concrete, limestone, freeze/thaw, CaO/MgO ratio, Al 2 O 3, ACR. 1. Introduction Limestone and granite are generally used as coarse aggregate in concrete mixtures. It mostly depends on the geographical area what type of coarse aggregate is commonly used in concrete mixtures. In Estonia, majority of the coarse aggregate used in concrete mixtures is limestone. In general, concrete, as a building material, is widely used and therefore profoundly examined but still lot of damaging effects appear during exploitation and therefore service life of material will be an unknown dimension. The fact that approximately 75%~80% of the concrete volume consists of aggregate makes the quality of coarse aggregate considerably important described by Neville [1]. According to EN 206, Table F.1 (Table 1) [2] recommendations, the only criterion for the coarse aggregate is frost resistance, but as a result of this research, submitted requirement is not sufficient to fulfill requirements for frost resistant concrete. In regions where air temperature stays at freezing Corresponding author: Eneli Liisma, Ph.D. student, research fields: concrete studies and renovation of buildings. eneli.liisma@ttu.ee. temperatures for long periods, one of the major problem concerning concrete durability is the freeze-thaw resistance. Concrete by its nature has a porous structure and, in case of wet surroundings, fluid ingress through the capillary pores will start. The freeze-thaw deterioration of concrete was firstly explained in 1945 by Powers [3] with hydraulic pressure theory and complemented in 1953 with osmotic pressure theory by Powers and Helmuth [4]. In the following several years, many researches have been proposing new theoretical ideas to explain the behavior of concrete during freeze-thaw cycles, for example pore pressure in 1998 by Penttala [5], propagation of freezing by Zuber and Marchand in 2000 [6] and degradation in stiffness by Hasanet et al. [7] in It is important to mention that all these theories actually describe the freeze/thaw process in cementitious material in concrete structure and the coarse aggregate is considered frost resistant by default. In this paper, freeze/thaw damaging process of frost resistant concrete is examined with poor quality of limestone aggregate and therefore substantial cause of

2 Damaging Formula of the Frost Resistant Concrete with Poor Quality of Coarse 599 the concrete damaging is explained. Poor quality of limestone is described with sufficiently low percent of lime (CaO), high content of magnesium oxide (MgO) and aluminium oxide (Al 2 O 3 ) with a considerably high percent of water absorption. According to several authors, coarse aggregates with water absorption higher than 2.0% by mass are considered not frost resistant. In addition to water absorption, there are specific chemical reactions that should be taken into account as a deleterious process in concrete structure with moist environment in present. Limestone as a carbonated rock is responsive to ACR (alkali-aggregate reaction) when humid conditions appear. Based on Katayama s work [8], the ACR is divided into three classes: (1) the ACR of dolomitic limestone that results in dedolomization; (2) the ACR of non-dolomitic limestone that produces rims; (3) ASR (alkali-silica reaction) of various carbonate rocks. One of the most likely cause of the coarse aggregate expansion by Katayama s explanation is the ASR of the cryptocrystalline quartz hidden in the argillaceous dolomitic limestone. Additionally, no expansion cracks were detected in dedolomitization process when ASR was not involved. All further tests by Katayama showed that ASR gel was the main reaction product that caused expansions and cracks in concrete structures. Grattan-Bellew et al. [9] stated in 2010 that ACR equals ASR. According to Beyene et al. [10] in 2013, the main mechanism of concrete distress and cracking in a concrete made with ACR susceptible aggregates (dark gray, fine-grained argillaceous dolomitic limestone) is ASR, not ACR. Based on Swenson et al. [11], ACR occurs if the alkali content in the cement is above 0.40%. This theory is supported by research work by Shehata et al. [12] alkali content (Na 2 O e, wt.% (weight percentage)) from PC (Portland cement) is one of the major sources of alkalis in concrete: CaMg(CO 3 ) 2 + 2XOH (+H 2 O) Mg(OH) 2 + CaCO 3 + X 2 CO 3 X is an alkali element such as potassium (K), sodium (Na) or lithium (Li). MgCO 3 is transformed into brucite that congests around in layers around rhombs that cause considerable expansion. The purpose of this paper is to show that frost resistance of concrete with poor quality of limestone is affected not only by the frost resistance and the water absorption of coarse aggregate but even more intensively the ACR of coarse aggregate. 2. Experimental Setup 2.1 Tests with Concrete The essential feature of the intended experiment consists of concrete mixtures which are made with equal slump (according to EN 206, Slump Class S2: 50~90 mm) and EN 206, Table F.1 recommendations were considered (maximal water/cement ratio, minimal class on compressive strength, minimal mass of cement and minimal percentage of entrained air) and frost resistant coarse limestone aggregate from Väo quarry (category of mass loss: F 2 ) to ensure frost resistant concrete. In addition, granite coarse aggregate with high quality was used. Bolomey formula was applied in designing the concrete components in mixtures. Cement Type CEM I 42.5 N, air-entraining agent REBAlit LP and superplastisizer Carboxyment 1860 were used in mixtures. Designed values for concretes Table 1 Exposure classes from EN 206, Table F.1. Limiting value Exposure class XF1 XF2 XF3 XF4 Maximum water/cement ratio Minimal class of compressive strength C30/37 C25/30 C30/37 C30/37 Minimal mass of cement (kg/m 3 ) Minimal percentage of entrained air Requirements for the aggregate Must be frost resistant

3 600 Damaging Formula of the Frost Resistant Concrete with Poor Quality of Coarse used in the research are presented in Table 2. Two types of specimens were made: mm 3 for compressive strength and mm 3 for scaling test. All concretes were kept 28 days in normal conditions (+20 C and relative humidity min 95%) before testing compressive strength and freeze/thaw cycle testing. Scaling test specimens were made according to Estonian national standard EVS 814:2003 and, in addition to standardized cut slabs, moulded surface specimens were tested. 2.2 Tests with Coarse Aggregate Determination of resistance to freezing and thawing of coarse aggregate was tested according to EN :2007. Determination of particle density and water absorption was tested according to EN :2013 and chemical analysis of coarse limestone aggregate was investigated according to EN : Test Results and Discussions The scaling mass loss of concretes presented in Figs. 1 and 2 show that concretes with saline environment (3% NaCl) have significant defects comparing to distilled water used in freeze/thaw process. All concretes were designed as frost resistant concretes as presented in Table 2, but only freeze/thawing in non-saline environment fulfils the requirements for the named exposure classes as shown in Table 3. According to EVS 814:2003, structure scaling (S 56 ) for exposure classes XF3 and XF4 after 56 freeze/thaw cycles must be at least equal or lower than 0.20 kg/m 2. If the first criterion is not fulfilled, the second criterion stipulates the scaling (S 56 ) after 56 freeze/thaw cycles at least equal or lower than 0.50 kg/m 2 with the scaling ratio of S 56 /S 28 lower than 2. Concretes with limestone coarse aggregate are deteriorated only on top of the coarse aggregate cementitious material was not detected Table 2 Mix proportions. Mix CS (MPa) ExpC W/C Cem (kg/m 3 ) C-Ag (kg/m 3 ) F-Ag (kg/m 3 ) W (kg/m 3 ) SP (%) A-E (%) 1 XF , C30/37 2 XF , CS class of compressive strength; ExpC exposure class; W/C water/cement ratio; Cem cement; C-Ag coarse aggregate; F-Ag fine aggregate; W water; SP superplastiziser; A-E air entraining agent Mass loss (kg/m 3 ) LS S GR S LS UC GR UC Freeze/thaw cycles Fig. 1 Test results of external damages of concrete after freeze/thaw experiment in distilled water. LS-S concrete with limestone coarse aggregate (cut by standard); LS-UC concrete with limestone coarse aggregate (uncut surface); GR-S concrete with granite (cut by standard); GR-UC concrete with granite (uncut surface).

4 Damaging Formula of the Frost Resistant Concrete with Poor Quality of Coarse 601 Mass loss (kg/m 3 ) Freeze/thaw cycles LS S GR S LS UC GR UC Fig. 2 Test results of external damages of concrete after freeze/thaw experiment in saline environment (3% NaCl). Table 3 Exposure classes and scaling criteria according to EVS 814:2003. Criteria of mass loss (kg/m 2 ) measured by scaling after 56 cycles Exposure class Distilled water 3 % NaCl sodium S XF or - S and S 56 /S 28 < 2 XF2 - XF3 XF4 - S or S and S 56 /S 28 < 2 S or S and S 56 /S 28 < 2 - S or S and S 56 /S 28 < 2 (a) (b) (c) (d) Fig. 3 Visual defects of frost resistant concrete: (a) typical pop-up defect after freeze/thaw cycles in distilled water on uncut slab; (b) pop-up defect after freeze/thaw cycles in saline water with larger cover area; (c) cut concrete specimen pop-up defect after 14 freeze/thaw cycles; (d) cut slab coarse aggregate defect after 14 freeze/thaw cycles.

5 602 Damaging Formula of the Frost Resistant Concrete with Poor Quality of Coarse CaO/MgO C1 C2 H V K N K Al 2 O 3 Fig. 4 Model of chemical composition as a basis for determining potential alkali carbonate reactivity of quarried carbonates (from CSA A A) tied to Estonian limestone quarries. C1 Criterion 1 for expansive zone; C2 Criterion 2 for expansive zone; H Harku quarry; V Väo quarry; K Karinu quarry; N Narva quarry; K Kunda quarry. damaged. Therefore, concretes with coarse limestone aggregate in saline environment are receptive for extra exposure potential alkali carbonate reaction. Typical pop-up damages of concrete structure are presented in Fig. 3. Comparing Estonian limestone to potential ACR model showed in Fig. 4, we can see that Estonian limestone from different quarries is mostly in an active expansive-zone between Criteria 1 and 2. 4.Conclusions Structure damages with poor quality of coarse aggregates used in frost resistant concrete are notably higher than those with granite coarse aggregate. Estonian origin limestone coarse aggregate tends to have chemical properties that most likely produce expansive reactions that will appear as structure damages of concrete. Therefore, potential alkali carbonation can be predicted from the limestone component proportion of CaO/MgO ratio and Al 2 O 3. The deterioration mechanism of concrete appeared mostly as a pop-up damage of expanded coarse aggregate that refers to firm cementitious structure and weak coarse aggregate performance. All in all, it is important to point out that the recommendations of the European standard EN 206 limiting values for composition and properties of concrete are suitable for cementitious materials, but insufficient for coarse aggregates. According to the test results, Estonian origin limestone coarse aggregate should be avoided in frost resistant concretes due to potential expansive process in concrete structure, even if frost resistance requirement of coarse aggregate is fulfilled. Acknowledgments The research has been conducted as part of the IUT1-15 project Nearly-Zero Energy Solutions and Their Implementation on Deep Renovation of Buildings financed by Estonian Research Council. References [1] Neville, A. M Properties of Concrete. UK: Longman Scientific & Technical, Ltd. [2] European Norm EN 206:2014, Concrete Specification, Performance, Production and Conformity. UK: British Standards Institution. [3] Powers, T. C A Working Hypothesis for Further Studies of Frost Resistance of Concrete. Journal of the American Concrete Institute 16 (4): [4] Powers, T. C., and Helmuth, R. A Theory of

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