Nội dung

Vietnam Journal of Mechanics , VAST , Vol.30, No.2 (2008), pp. 99 - 111 RESEARCH ON MANUFACTURING DRY MIXED CEMENT MORTAR WITH HIGH COMPRESSIVE STRENGTH, HIGH FLEXURAL STRENGTH, LOW SHRINKAGE AND HIGH WATERTIGHTNESS FOR RESTORATION OF DAMAGED HYDRAULIC STRUCTURES IN VIETNAM Nguyen Quang Phu 1 12 , Hoang Pho Uyen 3 , Jiang Lin Hua 1 , Liu Jiaping 4 1 College of Materials Science and Engineering, Hohai Unive rsity, Nanjing, P.R. China (210098) 2 Faculty of Hydraulic Engineering of Water Resources University, Vietnam 3 Research of Building Material Science Department, Institute of Water Resources Research, Vi etnam 4 Jiangsu Research Institute of Building Science, Nanjing 210008, China . Abstract. Usi ng normal materials to manufacture the mixed mortar is necessary for restoration of hydraulic structures in Vietna m . It will salvage the materials and decreases the cost price of the mortar. In this research, we used cement m ade in Vietnam (Chinfon - Haiphong cement), na tural sand (Lo River sand), polymer acrylic and high range water reducing (of SIKA company)' with proportion 1 : 3 : 0.03 : 0.003 by weight. The water to cement ratio is 0.5 , which always ensure t he compressive strength of mortar more t han 40 MPa and small shrinkage, good watertightness, and high adhesion. That is suitable for the restoration of concrete structures in general and hydraulic structures in particular of Vietnam. The dry mixed mortar is manufactured and in bag of 15±0.5 kg weight. Keywords: dry mixed cement mortar , compressive strength , shrinkage, flexural strength , adhesion , watertightness , high range water reducing admixt ure (HRWR), polymer acrylic. 1. INTRODUCTION After fifty years, many hydraulic structures in Vietnam were damaged and downgraded that why it is necessary to repair them for continuing operated. Here the most important hydraulic structures are made of concrete and reinforced concrete, that when repairing has required the same m aterials having the same fundamental properties. In order to repair those structures, the mort ar from cement with high compressive strength, no shrinkage, and high watertightness is used [1]. The mixed mortars have good properties of some overseas companies are available in Vietnam, but they are very expensive, so they are not suitable for Vietnam situation. Actually, the materials needed to manufacture these mortars are available in Vietnam and we can use them to make a kind of mixed mortar using to repair the damage of structures in general , hydraulic structures in particular. To produce this mixed mortar we can use usual materials Vietnam's . 100 Nguyen Quang Phu, Hoang Pho Uyen, Jiang Lin Hua, Liu Jiaping 2. RESEARCH OBJECTIVES The objective is to manufacture the mixed cement mortar which has high compressive strength, high flexural strength, low shrinkage and high watertightness in order to repair hydraulic concrete structures and reinforced concrete structures. The mortar should have following properties: · + High watertightness + Good slump for application + The good adhesion with the parent concrete and mortar + High compressive strength(!~ 2:40 MPa). 3. MATERIALS 3.1. Cement Chinfon Portland cement PC 40 made in Hai Phong, Vietnam. Its physical properties are shown in Table 1 Table 1. Physical properties of Portland cement PC40 Chinfon - Haiphong No 1 2 3 4 Item Compressive strength, 28 days Flexural strength , 28 days Setting time: Initial;Final Specific gravity Unit MP a MP a minute (g/cm 0 ) Result 42 6.0 113 ; 190 3.10 3.2. Fine aggregate (sand) In this research, we used the standard sand and the crush silicon sand. The results were very good, but the cost price was very high , therefore we have taken the river sand for experiments [2]. Namely, we used Lo River sand which has some properties as shown in Table 2. Table 2. Properties of fine aggregate (sand) No 1 2 3 4 Item Bulk specific gravity on oven-dry basis Apparent specific gravity SSD* Absorption Fineness modulus SSD*: Saturated surface-dry Unit (g/cm 0 ) (g/cm 0 ) % Result 2.65 1.45 0.4 2.54 The sand is sieved to reject the grains size > 5 mm. Then it was dried by the oven in temperature of 100-150°C for five hours until the humidity of sand equal zero percent. The sand was packed and kept in the dry condition. 3.3. Polymer Polymer acrylic is admixture in form of. powder, dry, white color, odorless. It is easy to dissolve in the water. The chemical function of Polymer acrylic as shown following [3]: Research on manufacturing dry mixed cement mortar ... 101 (-CH2-CH-)n I COOH 3.4. High range water reducing admixture (HRWR) High range water reducing admixture has the brand name ~f Mighty [3]. The main component of Mighty is naphthalene formaldehyde sulphonated. This admixture is being sold in Vietnam. 4. MIXTURE PROPORTION 4.1. Design preliminary proportion mortar The mortar using in concrete structures and reinforced structures must have high compressive strength (the compressive strength of mortar and the compressive strength of mortar matrix in old concrete · is equivalent). However, the polymer mortar has not strength function; in research we designed the proportion mortar was used in compliance with 14 TC~ 80-2001 and TCXD 2000 - Building standard [4, 5]. The compressive strength of mortar is calculated by following Eq. (1) fvI =A.JcI (c ) W - 0.8 , (1) where: A expresses materials quality, A=l.05 for materials of good quality, A=0.90 for materials of normal quality, anrl A=O. 75 for materials of low quality. f~ is the required compressive strength of mortar, f~ is the compressive strength of cement, C and W are respectively the amount of cement and water in 1 m 3 of the mortar. The cement content is calculated by Eq. (2) c= 1000 W n -+-+1 (2) Pc C Ps where: Pc, Ps are respectively the bulk specific gravity on oven-dry basis of cement and sand, n is the sand to cement ratio by weight, n = (Cf S); S is the sand content in 1 m 3 mortar, (C/S) can be chosen in graph of appendix A.2 of the standard branch 14TCN 80-2001. Then we can calculate the .proportion of mortar as follows: 1: S/C: W/C = 1 : 3.0: 0.50 In other hand, the high range water reducing admixture and polymer acrylic are used with the amount of 0.2-0.33 and 2-33, respectively. 4.2. The experimental scheme method In this project, we used the experimental scheme method with the orthogonal central turn of two levels and two factors to aim building the statistical mathematics model, based on that to access the effects of factors on the properties of mortar; such as the plasticity, compressive strength, flexural strength, adhesion between the old concrete and new mortar, saturated absorption; thence finding the optimal percent of polymer and HRWR. of real variables and coded variables are presented in Table 3. Nguyen Quang Phu, Hoang Pho Uyen, Jiang Lin Hua, Liu Jiaping 102 Table 3. The experimental scheme No 1 2 3 4 5 6 7 8 9 10 11 12 Real variables Coded variables X2 X1 -1 1 -1 -1 -1 1 1 1 0 0 1.414 0 -1.414 0 -1.414 0 1.414 0 0 0 0 0 0 0 ~l 6(3) (3) 1 1 3 3 2 2 0.6 2 3.6 2 2 2 0.30 0.20 0.20 0.30 0.25 0.37 0.25 0.18 0.25 0.25 0.25 0.25 X2 (9) 0) p, p, + 1.4 t4 +I ® .1 G) C!:i) © +I G) -I 0) ® + 1.4 IJ QJ '.!_!) -1.<-11·1 X1 (D -1 .4 t 11 s, Fig. 1. Sketch of the experimental scheme method with the orthogonal central turn of two levels and two factors In the experimental scheme method with two levels and two factors, as signed the percent of HRWR (% of cement content) is 6 and the percent of polymer (% of cement content) is 6. For establishing the experimental scheme the real variables ~1 and 6 are encoded to become the coded variables X1 and X2 (see [6]). The value of the coded variables are chosen in the range of (-1) and (+1), at the centre point of experimental scheme (0), and the values on the axis X 1 and X2( +oo, -oo) to make the rotation of the orthogonal scheme central turn. The sketch of the experimental scheme method with two levels and two factors as shown in Fig. 1 and the scheme Research on manufacturing dry mixed cement mortar ... 103 4.3. Research diagram To research the effects of the admixture on some properties of mortar, we issue the diagram for experiments. The di agram is shown below. Choose proportion of HRWR and polymer Design preliminary proportion high performance mortar i.- Research properties of materials ! ! Research effects of the admixtures on setting time --+ ,.. of mortar Research effects of the admixtures on slump of ' mortar l Research effects of the admixtures on compressive and bending strength of mortar .J. Research effects of the admixtures on capillary pore of mortar ! Research effects of the admixtures on adhesion of mortar + Research effects of the admixtures on the length of mortar bar ! Research effects of the admixtures on watertightness of mortar l . Propose manufacturing technology of dry mortar J Stop 5. RESULTS AND DISCUSSIONS 5.1. The effects of Polymer Acrylic on setting time of mortar The setting t ime of mort ar with 03, 13, 23, and 33 percentage of Polymer Acrylic are shown in Table 4, respectively. 104 Nguyen Quang Phu, Hoang Pho Uyen, Jiang Lin Hua , Liu Jiaping Table 4. The results of setting time of mortar 3 Acrylic Setting time (minutes) Initial Final 0 1 113 i90 118 198 2 3 125 ' 195 115 196 From the results in Table 4 we can see that using Polymer Acrylic of percentage (1-3 3) didn't affect the setting time of mortar. 5.2. The effects of Polymer Acrylic and HRWR on slump of mortar The slump of the mortar (D 2) is measured by the flow of mortar on shaking table according to 14TCN 80-2001. The function of regression represents the effects of polymer Acrylic and HRWR on slump of mortar is shown in Eq. (3). The results of flat diameter of mortar are shown in Table 5. D2 = 158.75 + 2.32X1 - 2.97X2 - 4.31Xf + 0.69Xi- 4.75X1X2, (3) where: D2 is the flat diameter of mortar; X 1 and X2 are the coded variables. Table 5. The flat diameter of mortar specimens No Control 1 2 3 4 5 6 7 8 9 10 11 12 D2 (mm) 190 163 152 156 148 161 156 165 145 156 164 158 152 3 100 86 80 82 78 85 82 87 76 82 86 83 80 Note: The flat diameter of mortar with the presence of polymer and HRWR is less than the control specimen (about 133 to 243) but they ensure good slump for application in Vietnamese climate condition and the accordance in 14TCN 80-2001. 5.3. The effects of the admixtures on compressive strength of mortar The mortar specimens are moulded in prismatic mould with 160 mm length and 40x40 mm cross section. After 24 hours , they are demoulded and cured in the curing room at humidity 803 and temperature 25 ± 2°C. The specimens are tested to determine compressive strength and flexural strength at ages of 3, 7, and 28 days . Research on manufacturing dry mixed cement mortar ... 105 The compressive strength of mortar of 3, 7 and 28 day-ages are shown in Table 6. The compressive strength of mortar are repres ented by Eq. (4), (5) and ( 6) J~, 3 = 32.535- 0.5 75X1+0.707X2 + 0.297Xf- 0.803Xi + 0.277X1X2 , (4) !L 7 = 35.534 + 0.41 7X1 + 0.119X2 + l.166Xf + l.982Xi + 0.893X 1X2 , (5) f~, 28 43.937- 0.436X1 + 0.997X2 + l.044Xf - 0.329Xi + l.723X1X2, (6) = where: J~ 3 , f~ 7 , !~ 28 is the compressive strength of mortar at 3, 7 and 28 days; X1 and X2 are tl;e coded v'ariables Table 6. The compressive strength of mortar at given ages No Control 1 2 3 4 5 6 7 8 9 10 33.1 12 7 days 3 days f~ 3 (MPa) 30.1 29.3 32.0 33.4 31.9 32 .8 33.5 30.8 33.7 32.0 31.6 110 32.9 % 100 97 106 111 106 109 111 102 112 106 105 38.2 109 J~ 7 (MPa) 35.1 35.3 37.3 36.8 38.4 36.4 40.9 41.8 38.2 40.6 35.7 109 31.9 28 days % 100 101 106 105 110 104 117 119 109 116 102 45.4 91 f~ 28 (MPa) 43.7 40.3 43.8 44.3 47.7 47.9 45.5 43.9 47.9 44.0 42 .8 104 39.7 % 100 92 100 101 109 110 104 100 110 101 98 91 Not e: From the results of compressive strength (see Table 6) we can see that the presence of polymer and HRWR doesn't affect on the compressive strength, and after 28 days the difference of compressive strengths of these mortars is negligible. With W / C = 0.5, the compressive strength of mortar is usually more than 40 MPa . However , when the admixtures content is high, the compressive strength of mortar attains 4 7.7 MP a, higher than control mix about 93. 5.4. The effects of the admixtures on flexural strength of mor tar The flexural strength of mortar at the given ages is shown in Table 7. The effects of the admixtures on the flexural strength of mort ar are represented by Eq. (7), (8) and (9): f~, 3 = 7.772 - 0.195X1 - 0.261X2 + 0.146Xf - 0.389Xi - 0.267X1X2 (7) f~, 7 = 8.361 - O.Ol6X1 + 0.222X2 + 0.547 Xf + 0.067 Xi+ 0.117 X1X2 (8) f~, 28 = 8.788 - 0.071X1 + 0.333X2 + 0.416Xf + 0.023Xi - X1X2 (9) where: J~ 3 , J~ 7 , J~ 28 is the flexural strength of mortar at 3, 7 and 28 days; X 1 and X 2 are the c~ded 'varia'bles. 106 Nguyen Quang Phu, Hoang Pho Uyen, Jiang Lin Hua, Liu Jiaping Table 7. The flexural strength of mortar at given ages No f~ 3 Control 1 2 3 4 5 6 7 8 9 10 11 12 3 days (MPa) 6.7 7.5 8.5 8.6 6.5 6.9 8.4 7.3 7.3 6.5 7.8 8.7 7.9 % 100 112 127 128 97 103 125 109 109 96 116 130 114 7 days f~ 7 (MPa) 8.0 8.8 8.7 8.2 8.9 8.2 9.4 8.1 10.1 9.6 8.8 8.4 8.1 % 100 111 109 103 111 102 118 101 127 120 110 105 102 28 days f~ 28 (MP a) 10.12 8.14 9.14 9.77 9.27 8.75 9.56 8.12 9.53 9.40 8.91 9.06 8.42 % 100 80 90 97 92 87 94 80 94 93 88 90 83 Not e : Compared with control specimen, the flexural strength at 28 days of specimen containing polymer and HRWR are little lower, (about 90 3 of flexural strength of the control specimen). This reason is the effects of polymer on the structure of cement matrix. However, increasing the density and decreasing the capillary pore of mortar to increase watertightness is aimed , so that the suitable percent of admixtures is necessary to use. 5.5. The effects of the admixtures on the adhered strength to parent mortar of mortar The adhesion of mortar to parent mortar at 28 days as shown in Table 8. Tabl e 8. The adhered strength of mortar at 28 days NO Control 1 2 3 4 5 6 7 8 9 10 11 12 28 days f~ 28 (MP a) 4.3 4.8 5.2 5.7 6.6 6.4 4.3 5.1 6.2 4.9 6.8 4.8 5.7 % 100 109 120 132 152 147 99 118 142 112 157 111 132 Research on manufacturing dry mixed cement mortar ... 107 The effects of the admixtures on the adhesion of mortar is shown by Eq.(10): = 5.933 - 0.279X1 + 0.274X2 - 0.229Xf - 0.037 Xi f~ , 28 . • - 0.332X1X2 (10) I where: f~ , 28 is the adhesion strength of mortar at 28 days; Xi and X2 are the coded variables Note: Using polymer and HRWR in mixed mortar increases the adhesion strength of mortar (about 10% to 57%) (see Table 8). We can see. that, with the proportion of high range water reducing is 0.225 % and polymer is 2.5%, the adhesiori strength is 6.6 MPa, that is higher than 52% comparing with control specimen. 5.6. The compressive strength of mortar on compacted sub-grade The compressive strength of mortar on compacted sub-grade at the given ages (3 , 7 and 28 days) is shown in Table 9. Table 9. The compressive strength of mortar at given ages No Control 1 2 3 4 5 6 7 8 9 10 11 12 3 days f~ 3 {MPa) 18.0 18.2 23.4 24.4 21.2 26.6 21.7 26.9 22 .3 26.0 27.3 19.9 23 .0 7 days % 100 101 130 135 118 148 121 149 124 145 152 111 128 f~ 7 (MPa) 34.5 29.5 32 .2 34.8 30.7 30.0 29.8 30.1 34.1 36.6 31.5 32.1 27.8 28 days % 100 86 93 101 89 87 86 87 99 106 91 93 81 f~ 28 {MPa) 41.0 38.9 36.3 39.2 40.1 37.7 36.0 37.0 41.0 46.2 38.5 40.2 37.6 % 100 95 89 96 98 92 88 90 100 113 94 98 92 The effects of the admixtures on the compressive strength of mortar on compacted sub-grade are represent ed by Eq. (11), (12) and (13): f~, 3 = 24.217 - 1.142X1 + 0.35 3X2 - 1.721Xf + 0.513Xi + 0.517 X1X2 (11) f~, 7 = 30.11 - 1.624X1+1.622X2 + 0.721Xf + 1.404Xi - 0.367X1X2 (12) f~, 28 = 37.834 - 0.356X1 + 0.143X2 + 0.104Xf + 1.487 Xi - 0.4X1X2 (13) where: f~ 3 , f~ 7 , f~ 28 are the compressive strength of mortar on compacted sub-grade at 3, 7 and 28 d~ys; X1 and X2 are the coded variables Note: Polymer and HRWR affect little on the compressive strength of mortar on compacted sub-grade as prescribed in TCVN (Vietnamese standard). The compressive strength is more than 30 MPa at 28 days, that can reach the target in the project. We can see that the range of HRWR content from 0.2% to 0.3 % doesn't influence on compressive Nguyen Quang Phu, Hoang Pho Uyen, Jiang Lin Hua, Liu Jiaping 108 strength on compacted sub-grade . So that the water to cement ratio chose, (W/C = 0.50) is suitable. 5. 7. The effects of the admixtures on capillary pore and saturated absorption of mortar The capillary pore and saturation absorption of mortar are given in Table 10 Table 10. The capillary pore and saturated absorption of mortar No Control 1 2 3 4 5 6 7 8 9 10 11 12 Note: WT dry, WT dry WT saturated (g) 570.2 567.0 563.2 577.3 553.7 566.8 571.7 575.2 546.2 553.7 552.7 554.8 564.7 WT saturated (g) W '1 saturated - W '1 dry WTdrv % 100 Capillary pore % 591.0 3.65 8.2 582.7 2.77 6.2 577.7 2.57 5.8 589.5 2.11 4.8 568.5 2.67 6.0 583.0 2.86 6.4 583.5 2.06 4.6 588.8 2.36 5.3 2.71 561.0 6.1 566.8 2.37 5.3 564.3 2.10 4.7 570.2 2.78 6.3 2.23 577.3 5.0 are weight of dry and saturated specimens, respectively. The effects of the admixtures on the saturation absorption of mortar are represented by Eq. (14) (14) where: Ds is the saturation absorption of mortar; X 1 and X2 are the coded variables Note: In comparison with the control specimen, the capillary pore of specimens with admixtures is lower about 20% to 403 . Therefore the presence of polymer and HRWR in mixed mortar increases its watertightness (see Table 10). 5.8. The effects of the admixtures on the length change of mortar bar The length change of mortar bar is measured in compliance with [7]. The specimens are casted and cured in the humidity of 80% and temperature of 25±2°C (condition in Vietnam). Symbol Mo relates to specimen without admixtures; M 1 relates to specimen containing 3% polymer acrylic and 0.3% HRWR. The results of the length change of mortar bar for some given ages are represented in Table 11 and Fig. 2. After 28 days, the shrinkage of control mortar (M 0 ) is 0.41 %; this result is complied with some other research results [8, 9, 10] . In that time, the specimen containing 3% polymer acrylic and 0.3% HRWR (M1) has the shrinkage of 0.06% that is very small. Thus, the adhesion to parent mortar of the mortar containing admixtures (polymer and HRWR) is higher than that of the mortar without admixtures. So that, the polymer acrylic