THE UNIVERSITY OF DA NANG UNIVERSITY OF SCIENCE AND TECHNOLOGY NGUYEN BA THACH AN EXPERIMENTAL STUDY ON SHRINKAGE STRAINS OF CONCRETE IN STANDARD CLIMATIC CONDITIONS AT GIA LAI MAJOR : ENGINEERING MECHANICS CODE : 9520101 SUMMARY OF DOCTORAL DISSERTATION IN THE FIELD OF ENGINEERING DA NANG - 2019 The work was finished at University of Science and Technology - The University of Da Nang Supervisors: Dr TRUONG HOAI CHINH, Assoc Prof Dr PHAN QUANG MINH, Prof Reviewer 1st : ………………………………… Reviewer 2nd: ………………………………… Reviewer 3rd: ………………………………… This dissertation was examinedby the Committeeat The University of Da Nang on … of …, 20… For the details of the dissertation, please contact: - Information and Library Center, University of Da Nang - National Library of Viet Nam INTRODUCTION Motivation and thematic framework Scientists all over the world have been studying the time-dependent shrinkage of concrete for long time and achieving many important results There are many scientific research projects, many scientific articles in prestigious magazines which introducethe research results of shrinkage strains The contents of researches include: Study on shrinkage strain of new concrete material; Research on the solutions of reducing shrinkage strains (using of admixtures, new materials, etc.) The researchers conducted these studies based on the experimental measurements of the shrinkage strains of concrete materials Currently, the prediction for shrinkage is mainly depended on the Foreign Standards which have less reliable estimationin risks and different temperature climatic conditions The current standards of developed countries, such as Eurocode European Standard (EC2, 1992), British Standard 8110 (BS 8110, 1997), Standard CEB-FIP 1990 (CEB 1990), American Standard (ACI-209), Australian Standards 3600 (AS 3600), Forecast model of Russian Concrete Institute, Russian Standard (GOST 24544-81), present the details of the experimental works on measuring shrinkage strains of concrete There are a few researches of experimental shrinkage in Vietnam currently, and the experimental data are not systematic The determination of shrinkage strains for regular concrete without admixtures does not have specific experimental data which correspond to several climatic conditions of difference zones The crack due to shrinkage strains occurs commonly in construction works in Gia Lai province where the characteristics of the Central Highlands climate is obvious These cracks directly affect to the structures of building The study on the shrinkage strains of concrete in climatic conditions of Gia Lai province is essential to support the construction management, design consultancy, construction, using of concrete materials as well as the application of new technologies for reinforced concrete structures in the area Based on above analyses, the topic of this dissertation is “An experimental study on shrinkage strains of concrete in standard climatic conditions at Gia Lai” This is anessential and practical scientific research project Objectives of the research The experimental study systematically collected and built the experimental data on the shrinkage strain of concrete using local aggregate in standard climatic conditions of Gia Lai province These data are basically used to study on the design of reinforced concrete structures at Gia Lai suitably; The experimental study determined experimental coefficients based on suitable prediction model As a result, the development of time-dependent shrinkage strains of concrete in standard climatic conditions at Gia Lai could be predicted; The experimental study compared the shrinkage strains of concrete in standard and natural climatic conditions at Gia Lai As a result, the suitable solutions for restricting shrinkage strains of concrete in the first period after casting were suggested; The experimental study on shrinkage strains of reinforced concrete and steel fiber concrete proposed the solutions which could restrict shrinkage strains of concrete Object and scope of the thesis Object: Time-dependent shrinkage strains of concrete in standard climatic conditions of Gia Lai province; Effect of reinforced bars and steel fibers on shrinkage strains of concrete Scope of Works: Shrinkage strains of concrete without admixtures in standard climatic conditions of Gia Lai province with specimens: Regular concrete of compressive strength of concrete B22.5 (M300#) with ratios between water and cement (N/X) of 0.40, 0.45, 0.50; Steel fiber reinforced concrete (density of steel fiber is 40 kg/m3); Reinforced concrete with reinforcement ratio of 1.13% Methodology Theoretical research and experimental research Science and practical significance Science Significance: The thesis has studied the time-dependent shrinkage strains of concrete in the standard and natural climatic conditions of Gia Lai province The experimental coefficients which are used to predict the time-dependent shrinkage strains of concrete are determined As a result, the thesis supports the recommendations for researching the response of reinforced concrete structures considering the shrinkage strains Practical Significance: The time-dependent shrinkage strains of concrete in standard and natural climatic conditions of Gia Lai province are determined by the experimental results of this thesis These results provide a set of data on shrinkage strain of concrete which are used to support the analysis reinforced concrete structures considering the shrinkage strains Consequently, the recommendations of reducing the crack of concrete structures and reinforced concrete structurewere proposed Organization of the thesis The thesis comprises three chapters which are described as follow: Chapter 1: Theoretical researches on time-dependent shrinkage strains of concrete Chapter 2: An experimental study on shrinkage strains of concrete in climatic conditions at Gia Lai Chapter 3: To analyze and evaluate the experimental results Novelty of the thesis • The thesis built the experimental data on the shrinkage strain of concrete using local aggregate in climatic conditions of Gia Lai province These data are used in practical design of reinforced concrete structures • The thesis conducted experimental study on the shrinkage of concrete in 364 days with several specimens of the ratio between water and cement (N/X) of 0.40, 0.45 and 0.50 in standard climatic conditions of Gia Lai province (temperature of 25±20C and humidity of 75±5%) The results of experiment are used to predict time-dependent shrinkage strains of concrete in standard climatic conditions of Gia Lai province • The thesis conducted the experimental study on the comparison of the development of shrinkage strain of concrete between the standard and the natural climatic conditions of Gia Lai province Based on the experimental results, after 21 days of concrete casting, the shrinkage strains of concrete of natural climatic conditions of Gia Lai province are around twice times than that of standard climatic conditions • The thesis conducted the experimental study on the effect of steel fibers and steel bars on reducing the shrinkage strains of concrete Based on these results, the recommendation of reducing the shrinkage strains of concrete was conducted CHAPTER THEORETICAL RESEARCHES ON TIME-DEPENDENT SHRINKAGE STRAINS OF CONCRETE 1.1 Research background of time-dependent shrinkage strains of concrete in Vietnam and all over the world Practical researches on time-dependent shrinkage strains of concrete all over the world: The primary researches were published by many authors such as: Pickett (1956), Lyse (1960), Neville (1970, 1981, 1983, 1990, 1995), Smadi et al (1987), Bažant (1982, 1988, 1994), Tazawa Miyazawa (1995), Ojdrovic Zarghamee, 1996, Mac Gregor, 1997, Gilbert (2001), Acker Ulm (2001), Swapnil Deshpande et al (2007) Recently, there are some authors who published their researches such as: Faez Sayahi (2016), Vasu Krishna, Rakesh Kumar (2016), Balaguru, Caronia David, Roda Andrés (2017), Jun Yang, Qiang Wang, Yuqi Zhou (2017), Karagüler, Yatağan (2018), Safiuddin, Kaish, Woon, Raman (2018) Practical researches on time-dependent shrinkage strains of concrete in Vietnam: The research on shrinkage deformation of concrete can include a number of authors such as: Le Van Thuong (1993), Hoang Quang Nhu (2007), Cao Duy Khoi, Ngo Hoang Quan (2012), Nguyen Ngoc Binh, Nguyen Trung Hieu (2012; 2015), Tran Ngoc Long (2016) 1.2 Time-dependent shrinkage strains of concrete Shrinkage is a time-dependent strain of concrete associated with the loss of moisture that occurs at different stages in the life of the concrete It is independent with loading 1.3 Mechanism of shrinkage True shrinkage mechanism: Capillary shrinkage; Chemical shrinkage; Dry shrinkage Nominal shrinkage mechanism: Crack effect; Geometrical effect 1.4 Factors affecting shrinkage Internal factors: Aggregate; Cement; Ratio between water and cement; Chemical admixtures; Dimension and shape of specimens External factors: Curing method; Temperature; Relative humidity 1.5 The models of time-dependent shrinkage strains of concrete Main models for estimating time-dependent shrinkage strains of concrete in several standards include: Russian Standard GOST 24544-81, Prediction Model of Russian Concrete Institute, Australian Standards AS 3600, American Standard ACI 209R-92, British Standard BS 8110, European Standard CEBFIP 2010, European Standard Eurocode and model B3 1.6 Prediction formulations for time-dependent shrinkage strain of concretebased on the experimental resultsaccording to Russian standard GOST 24544-81 According to GOST 24544-81, the time-dependent shrinkage strain of concrete is determined by equation (1.1): ∆𝑡 𝛼𝑛 + ∆𝑡 1.7 Analysis of cracks due to shrinkage strain in concrete 𝜀𝑐𝑠 (𝑡) = 𝜀𝑐𝑠 (∞) (1.1) Cracking is one of the main reasons of impairment of working ability (including bearing capacity and utility), resulting in a reduction in the life of the building for concrete and reinforced concrete construction Shrinkage is divided into softening shrinkage and strengthening shrinkage (dry shrinkage) Softening shrinkage occurs within 24 hours (most significant in the first 10 hours) after concreting, when the strength of concrete is not enough For concrete materials, two time-dependent shrinkage strains are soft shrinkage strain and dry shrinkage strain Because of shrinkage strains, concrete is subjected to tensile stress which depends on the value of shrinkage strain 1.8 Effect of reinforcement bars in cracked reinforced concrete structures due to shrinkage strain Because of shrinkage strains, concrete is subjected to tensile stress which depends on the value of shrinkage strain, while reinforcement bars are in compressive stage The reinforcement bars reduce the extension of cracks instead of restricting cracks In conclusion, the position of reinforcement bars in reinforced concrete structures are to reduce the development of cracks 1.9 Conclusion of Chapter Scientists all over the world have been studying the time-dependent shrinkage of concrete for long time and achieving many important results The shrinkage of concrete has been studied over more than a century with several research aspects, from the basic mechanism of impact shrinkage to several structural problems related to strains Based on above analyses of mathematical models for time-dependent shrinkage strains of concrete, main factors which affect to shrinkage strains of concrete material includes: concrete mix method (type of cement, ratio of fine aggregate, ratio between water and cement, etc.), dimension and shape of structures, relative humidity of environment The suitable concrete mix design is important to reduce shrinkage strains of concrete Currently, the researches on shrinkage strains of concrete are few in climatic conditions of Gia Lai province There have been not experimental data of shrinkage strains for regular concrete without admixtures in Vietnam Standard Therefore, the research of determination of shrinkage strains of concrete is essential, and the topic of this thesis is determined CHAPTER AN EXPERIMENTAL STUDY ON SHRINKAGE STRAINS OF CONCRETE IN CLIMATIC CONDITIONS AT GIA LAI 2.1 Climatic characteristics at Gia Lai Standard climatic conditions at Gia Lai: According to Pleiku City Metering Station of the Central Highlands Hydrometeorological Agency, the average annual temperature is 230C-270C The average annual humidity is 70%-80% There fore, the standard temperature is 25±20C and the standard humidity is 75±50C Natural climatic conditions at Gia Lai: The temperature and humidity in Environmental Laboratory are observed during the experiments The temperature changes from 22.50C to 31.50C, while the range of humidity is 51% to 89% 2.2 Objectives of experiments Based on the set of experimental data results: Assessingthe effect of ratio of water and cement (N/X) on the shrinkage strains of regular concrete, steel fiber reinforced concrete and reinforced concrete; Evaluating the time-dependent shrinkage strains of regular concrete, steel fiber reinforced concrete and reinforced concrete in standard and natural climatic conditions of Gia Lai; Assessing the restriction of cracking due to shrinkage strain of concrete with steel fibers and reinforcement bars; proposing the experimental coefficients to determine time-dependent compressive strength, Young modulus and shrinkage strains of concrete 2.3 Experiment Experiments of determination the compressive resistance strength of concrete regard to shrinkage strain; Experiment of determination of time-dependent compressive strength and young modulus of concrete; Experiment of calculation of shrinkage strains of concrete; Experiment of measurement of restrained shrinkage of concrete by Restrained Ring Test 2.4 Materials used in experiments, making specimens, casting and maintenance of specimens Materials used in experiments: Cement; Stone (1x2); Sand; Water; Steel fiber; Reinforcement bar 12 Fabrication of specimens based on TCVN 3015:1993 Curing specimens based on TCVN 3117:1993 and TCVN 3015:1993 2.5 Experimental equipmentfor measuring shrinkage strainsof concrete Climatic cabinet (controlling temperature and humidity according to experimental requirements): Climatic cabinet is set up at temperature 25±20C, humidity 75±5% during the experiment These setups specify the average temperature and humidity of standard climatic conditions of Gia Lai Tools for measuring shrinkage strain of concrete: Comparator of MATEST (Italia) manufacture; Model: C363 KIT Dimension of specimens of determination the compressive resistance strength of regular concrete is 15x15x15 cm Dimension of specimens of determination the time-dependent compressive strength and young modulus of concrete is 15x30 cm Dimension of specimens of calculation of shrinkage strains of concrete is 10x10x40 cm Dimension of Restrained Ring Test tools are 406 mm of outer diameter, 305 mm of inner diameter, 152 mm of height and 12.5 mm of thickness 2.6 Experimental result Table 2.1 Experimental results of compressive strength 𝑹đ𝒄 𝒏 (𝟐𝟖) of regular concrete đ𝒄 The average value 𝑹𝒏 (𝟐𝟖) (MPa) No Symbol Note 28 days M1 31.52 Ratio of N/X = 0.40 (Regular concrete) M2 30.68 Ratio of N/X = 0.45 (Regular concrete) M3 29.05 Ratio of N/X = 0.50 (Regular concrete) Table 2.2 Experimental results of the time-dependent compressive strength Rn(t) of regular concrete Specimens group Ratio (N/X) M1 M2 M3 0.40 0.45 0.50 days 22.53 21.63 21.10 of M1, M2, M3 specimens The average value Rn(t), MPa 28 60 90 180 270 days days days days days 31.14 33.00 33.58 34.26 34.58 29.58 31.48 32.10 32.61 32.85 28.70 30.67 31.29 31.64 31.87 364 days 34.74 33.18 32.09 Standard deviation (STD) 4.34 4.09 3.93 Table 2.3 Experimental results of the time-dependent compressive strength Rn(t) of steel fiber Specimens group Ratio (N/X) MS1 MS2 MS3 0.40 0.45 0.50 reinforced concrete of MS1, MS2, MS3 specimens The average value Rn(t), MPa 28 60 90 180 270 days days days days days days 23.86 32.95 34.82 35.30 35.90 36.22 23.00 31.35 33.23 33.80 34.25 34.49 22.47 30.47 32.47 33.00 33.30 33.51 364 days 36.32 34.74 33.66 Standard deviation (STD) 4.46 4.18 4.03 Table 2.4 Experimental results of the time-dependent Young Modulus E(t) of regular concrete of M1, M2, M3 specimens The average value E(t), MPa Standard Specimens Ratio deviation 28 60 90 180 270 364 group (N/X) (STD) days days days days days days days M1 0.40 25225 32045 33164 33528 33830 34031 34432 3221 M2 0.45 22501 28988 30143 30396 30731 31042 31488 3112 M3 0.50 20281 25931 27018 27262 27432 27749 27999 2709 Table 2.5 Experimental results of the time-dependent Young Modulus E(t) of steel fiber reinforced Specimens group Ratio (N/X) MS1 MS2 MS3 0.40 0.45 0.50 days 26184 23421 21135 concrete of MS1, MS2, MS3 specimens The average value E(t), MPa 28 60 90 180 270 days days days days days 33215 34258 34537 34787 34943 30109 31244 31425 31698 31952 26987 28085 28250 28341 28618 364 days 35300 32352 28840 Standard deviation (STD) 3215 3120 2730 Table 2.6 Experimental results of time-dependent shrinkage strain and mass loss of concrete in standard climatic conditions of Gia Lai (Group - Regular concrete) Date Spec M1 N/X = 0.40 mM1 M1 Spec M2 N/X = 0.45 mM2 M2 Spec M3 N/X = 0.50 mM3 M3 Temperature Humidity (t) (RH) 14 21 (%) 0.27 0.38 0.45 0.51 0.57 0.61 0.69 0.72 (x10-6) 23 37 50 60 70 80 143 193 (%) 0.78 1.19 1.35 1.50 1.61 1.69 1.89 1.93 (x10-6) 33 50 63 77 90 107 183 243 (%) 1.61 2.09 2.25 2.38 2.47 2.52 2.85 3.10 (x10-6) 43 63 80 100 117 130 221 284 (oC) 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 (%) 75 75 75 75 75 75 75 75 75 28 35 42 49 56 63 70 77 0.75 0.79 0.90 0.99 1.03 1.07 1.11 1.14 237 273 303 330 357 377 397 407 1.95 2.01 2.05 2.09 2.13 2.16 2.21 2.25 290 330 363 390 410 430 447 463 3.15 3.22 3.31 3.37 3.41 3.44 3.48 3.52 337 378 408 434 458 478 494 508 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 75 75 75 75 75 75 75 75 84 91 1.17 1.21 423 437 2.28 2.33 477 487 3.55 3.57 521 531 25.0 25.0 75 75 98 105 1.24 1.26 450 453 2.36 2.38 500 507 3.60 3.62 541 553 25.0 25.0 75 75 Date Spec M1 N/X = 0.40 Spec M2 N/X = 0.45 Spec M3 N/X = 0.50 mM1 (%) M1 (x10-6) mM2 (%) M2 (x10-6) mM3 (%) M3 (x10-6) 112 119 1.28 1.30 470 473 2.41 2.43 523 527 3.65 3.67 126 133 1.33 1.35 487 493 2.45 2.47 537 543 140 147 1.37 1.39 503 507 2.49 2.50 154 168 182 196 224 252 280 322 364 1.40 1.43 1.47 1.50 1.56 1.61 1.67 1.75 1.84 517 523 530 537 550 563 577 603 610 2.53 2.56 2.60 2.63 2.68 2.74 2.79 2.87 2.95 Temperature Humidity (t) (RH) (oC) (%) 558 568 25.0 25.0 75 75 3.69 3.71 578 584 25.0 25.0 75 75 553 563 3.73 3.74 598 608 25.0 25.0 75 75 567 573 580 587 593 607 620 633 653 3.76 3.79 3.82 3.85 3.91 3.96 4.02 4.10 4.17 618 624 631 638 644 657 670 687 700 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 75 75 75 75 75 75 75 75 75 Table 2.7 Experimental results of time-dependent shrinkage strain and mass loss of concrete in standard climatic conditions of Gia Lai (Group - Steel fiber reinforced concrete) Date Spec MS1 N/X = 0.40 mMS1 MS1 (%) (x10-6) 0 0.35 13 0.52 20 0.65 33 0.72 50 0.78 60 Spec MS2 N/X = 0.45 mMS2 MS2 (%) (x10-6) 0 1.49 23 1.75 33 1.86 47 1.94 67 2.00 80 Spec MS3 N/X = 0.50 mMS3 MS3 (%) (x10-6) 0 2.58 33 2.75 47 2.89 63 3.03 90 3.18 107 Temperature Humidity (t) (RH) (oC) 25.0 25.0 25.0 25.0 25.0 25.0 (%) 75 75 75 75 75 75 14 21 28 35 42 49 56 0.84 1.00 1.04 1.11 1.16 1.23 1.30 1.34 70 100 123 157 193 229 254 278 2.05 2.18 2.21 2.24 2.28 2.34 2.43 2.47 97 140 173 210 251 282 311 330 3.29 3.42 3.49 3.57 3.64 3.69 3.75 3.81 120 177 213 257 297 333 357 377 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 75 75 75 75 75 75 75 75 63 70 1.38 1.43 297 313 2.51 2.56 350 366 3.85 3.89 397 410 25.0 25.0 75 75 77 84 1.50 1.53 323 337 2.60 2.67 380 390 3.93 3.97 424 437 25.0 25.0 75 75 Date Spec MS1 N/X = 0.40 Spec MS2 N/X = 0.45 Spec MS3 N/X = 0.50 mMS1 (%) MS1 (x10-6) mMS2 (%) MS2 (x10-6) mMS3 (%) MS3 (x10-6) 91 98 1.57 1.60 353 367 2.72 2.75 403 417 4.01 4.04 105 112 1.62 1.64 373 387 2.76 2.78 427 440 119 126 1.66 1.68 403 417 2.80 2.82 133 140 147 154 168 182 196 224 252 280 322 364 1.70 1.71 1.73 1.75 1.79 1.83 1.86 1.91 1.96 2.03 2.10 2.17 423 433 447 457 463 470 477 490 503 517 537 551 2.84 2.85 2.88 2.90 2.93 2.98 3.01 3.06 3.11 3.16 3.23 3.31 Temperature Humidity (t) (RH) (oC) (%) 447 457 25.0 25.0 75 75 4.06 4.07 473 484 25.0 25.0 75 75 457 467 4.09 4.11 497 507 25.0 25.0 75 75 473 483 497 508 513 520 527 534 541 560 567 593 4.13 4.15 4.17 4.19 4.22 4.26 4.29 4.34 4.39 4.45 4.53 4.60 514 527 540 557 570 579 586 596 604 613 637 651 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 75 75 75 75 75 75 75 75 75 75 75 75 Table 2.8 Experimental results of time-dependent shrinkage strain and mass loss of concrete in standard climatic conditions of Gia Lai (Group - Reinforced concrete) Date Spec MT1 N/X = 0.40 mMT1 MT1 (%) (x10-6) 0 0.65 0.98 12 Spec MT2 N/X = 0.45 mMT2 MT2 (%) (x10-6) 0 2.05 13 2.26 17 Spec MT3 N/X = 0.50 mMT3 MT3 (%) (x10-6) 0 3.06 23 3.29 30 Temperature Humidity (t) (RH) (oC) 25.0 25.0 25.0 (%) 75 75 75 14 21 28 35 1.14 1.22 1.35 1.40 1.50 1.56 1.61 1.67 20 37 43 53 77 93 110 130 2.34 2.40 2.44 2.47 2.55 2.64 2.68 2.73 30 57 70 87 111 123 143 173 3.43 3.52 3.58 3.62 3.80 3.88 3.94 4.02 47 80 97 110 140 167 193 223 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 75 75 75 75 75 75 75 75 42 49 1.70 1.75 157 183 2.79 2.84 200 233 4.14 4.21 257 280 25.0 25.0 75 75 56 63 1.79 1.82 203 220 2.88 2.92 250 270 4.25 4.29 297 317 25.0 25.0 75 75 11 Date Spec MS1 N/X = 0.40 Spec MS2 N/X = 0.45 Spec MS3 N/X = 0.50 mMS1 (%) MS1 (x10-6) mMS2 (%) MS2 (x10-6) mMS3 (%) MS3 (x10-6) 28 35 1.40 1.48 310 310 2.48 2.56 373 376 3.81 3.85 42 49 1.51 1.54 314 318 2.62 2.66 382 373 56 63 1.58 1.61 331 350 2.70 2.75 70 77 84 91 98 105 112 119 126 133 140 147 154 168 182 196 224 252 280 322 364 1.65 1.70 1.74 1.78 1.82 1.84 1.86 1.88 1.90 1.91 1.94 1.96 1.98 2.03 2.07 2.09 2.14 2.19 2.25 2.32 2.39 368 377 390 386 420 433 429 457 470 464 483 500 496 520 527 533 528 557 573 570 610 2.79 2.84 2.88 2.93 2.97 2.99 3.01 3.04 3.06 3.08 3.10 3.12 3.14 3.18 3.22 3.24 3.30 3.35 3.41 3.48 3.56 Temperature Humidity (t) (RH) (oC) (%) 426 433 23.5 29.1 77 61 3.91 3.96 436 420 23.3 23.8 70 77 370 413 4.00 4.04 418 460 22.6 26.2 81 63 430 445 453 449 480 490 484 520 530 526 547 560 553 580 587 593 587 607 623 619 660 4.09 4.13 4.17 4.21 4.26 4.28 4.30 4.33 4.35 4.37 4.39 4.41 4.43 4.48 4.51 4.57 4.62 4.67 4.72 4.80 4.87 474 487 503 499 524 538 532 564 577 571 601 614 609 643 653 662 658 686 692 693 720 28.8 22.5 30.8 24.3 27.2 23.3 22.8 27.6 30.1 23.2 26.7 28.3 23.6 30.5 29.2 31.5 23.5 29.2 28.2 27.4 29.5 55 89 52 77 62 78 83 58 53 82 66 60 80 55 58 51 80 56 58 60 55 Table 2.11 Experimental results of time-dependent shrinkage strain and mass loss of concrete in natural climatic conditions of Gia Lai (Group - Reinforced concrete) Date Spec MT1 N/X = 0.40 mMT1 MT1 (%) (x10-6) 0 0.89 34 Spec MT2 N/X = 0.45 mMT2 MT2 (%) (x10-6) 0 1.80 50 Spec MT3 N/X = 0.50 mMT3 MT3 (%) (x10-6) 0 3.26 67 Temperature Humidity (t) (RH) (oC) 28.8 28.2 (%) 56 57 1.16 1.29 54 70 2.09 2.34 74 90 3.56 3.65 94 115 29.6 29.0 53 55 1.46 1.56 82 94 2.41 2.51 107 123 3.76 3.84 140 162 31.2 30.7 51 52 12 Date Spec MT1 N/X = 0.40 Spec MT2 N/X = 0.45 Spec MT3 N/X = 0.50 mMT1 (%) MT1 (x10-6) mMT2 (%) MT2 (x10-6) mMT3 (%) MT3 (x10-6) 14 1.59 1.65 108 192 2.60 2.64 144 244 3.90 3.96 21 28 1.70 1.74 255 265 2.72 2.76 323 316 35 42 1.79 1.84 266 270 2.84 2.89 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 168 182 196 224 252 280 322 364 1.87 1.92 1.96 2.01 2.04 2.08 2.13 2.16 2.17 2.19 2.21 2.23 2.25 2.27 2.29 2.30 2.34 2.38 2.40 2.45 2.50 2.56 2.64 2.72 272 278 283 307 310 320 325 340 356 351 390 404 400 419 438 433 466 474 483 478 503 520 517 554 2.96 3.01 3.06 3.12 3.16 3.21 3.25 3.30 3.31 3.33 3.36 3.38 3.40 3.42 3.44 3.46 3.51 3.55 3.57 3.63 3.68 3.74 3.81 3.89 Temperature Humidity (t) (RH) (oC) (%) 179 298 28.6 29.2 56 54 4.01 4.05 378 366 24.7 23.5 72 77 320 324 4.11 4.17 370 355 29.1 23.3 61 70 312 310 333 347 360 372 364 397 410 404 443 460 456 478 493 490 523 532 539 532 567 577 573 600 4.22 4.28 4.33 4.38 4.43 4.48 4.51 4.55 4.56 4.59 4.61 4.63 4.66 4.68 4.70 4.73 4.77 4.81 4.84 4.88 4.93 4.99 5.06 5.14 343 350 380 390 403 421 414 442 457 450 493 507 503 530 544 541 579 596 607 602 636 643 640 673 23.8 22.6 26.2 28.8 22.5 30.8 24.3 27.2 23.3 22.8 27.6 30.1 23.2 26.7 28.3 23.6 30.5 29.2 31.5 23.5 29.2 28.2 27.4 29.5 77 81 63 55 89 52 77 62 78 83 58 53 82 66 60 80 55 58 51 80 56 58 60 55 Table 2.12 Date of beginning ofobserved cracks in concrete specimens of Restrained Ring Test Regular concrete (BTT) Specimen type Time of crack appearance Date CH1 CH2 CH3 Reinforced concrete fiber steel (BTCST) CH4 CH1 11 CH2 11 CH3 11 CH4 11 2.7 Conclusion of Chapter The process of making specimens, casting and maintenance of specimens was carried out based on the specification of TCVN 3015:1993 The process of measurement of shrinkage strains was specified in TCVN 3117:1993 13 The time-dependent compressive strength and Young modulus of concrete of specimens were measured within 364 days, which includes times of measurement of days, 28 days, 60 days, 90 days, 180 days, 270 days and 364 days The maximums of compressive strength and Young modulus were observed at 364 days The set of specimens for measurement shrinkage strains was keep in climatic cabinet of temperature of 25±2 C and humidity of 75±5% during the experiments The measurement of time-dependent shrinkage strains of concrete specimens was carried out after 364 days The experimental results of shrinkage strain of concrete specimens are the average value of three specimens In the date of 364 of measurement, the experimental results of shrinkage strains of concrete were from 610x10-6 to 700x10-6 Those resultsare quite high Experimental results of Restrained Ring Test indicated that the steel fiber had important role in restriction of crack due to shrinkage The steel fiber not only slow down the crack formation process but also reduce the expansion of crack As a result, the possibility of using steel fiber in reinforced concrete structures, especially floor of industrial builds, floor of bridges, etc to restrict the crack of concrete due to shrinkage strains is high CHAPTER TO ANALYZE AND EVALUATE THE EXPERIMENTAL RESULTS 3.1 Analyzing and evaluating time-dependent compressive strength Rn(t) and Young Modulus E(t) of two groups of concrete in natural climatic conditions (Group - Regular concrete; Group - Steel fiber reinforced concrete) 3.1.1 Analyzing and evaluating time-dependent compressive strength Rn(t) of two groups of concrete (Group - Regular concrete; Group - Steel fiber reinforced concrete) According to the experimental results of time-dependent compressive strength of regular concrete and steel fiber reinforced concrete, proposing the formulas and the experimental coefficients which indicate the relation between the compressive strength Rn(t) and the compressive strength of 28 days based on thetotal least-squares method (use the Solver tool in Microft Excel) 𝑡 𝑅𝑛 (𝑡) = 𝑅𝑛 (28) 3,08 + (0,89 𝑡) Table 3.1 The suggested results of compressive strength of concrete Rn(t) (Group - Regular concrete; Group - Steel fiber reinforced concrete) The average value Rn(t), MPa Standard deviation 28 60 90 180 270 364 (STD) days days days days days days days The suggested results of compressive strength of concrete Rn(t) (Group - Regular concrete) M1-ĐX 0.40 23.41 31.14 33.08 33.69 34.33 34.55 34.66 4.03 M2-ĐX 0.45 22.24 29.58 31.42 32.01 32.61 32.82 32.92 3.83 M3-ĐX 0.50 21.58 28.70 30.49 31.05 31.64 31.84 31.94 3.71 The suggested results of compressive strength of concrete Rn(t) Specimens group Ratio (N/X) (3.1) 14 The average value Rn(t), MPa 28 60 90 180 270 days days days days days days (Group - Steel fiber reinforced concrete) 364 days Standard deviation (STD) 0.40 0.45 24.77 23.57 32.95 31.35 35.00 33.30 35.65 33.92 36.32 34.56 36.55 34.78 36.67 34.89 4.26 4.06 0.50 22.91 30.47 32.37 32.97 33.59 33.80 33.91 3.94 Specimens group Ratio (N/X) MS1-ĐX MS2-ĐX MS3-ĐX Figure 3.1 The experimental results and Figure 3.2 The experimental results and suggested results of compressive strength of suggested results of compressive strength of concrete Rn(t) concrete Rn(t) (Group - Regular concrete) (Group - Steel fiber reinforced concrete) 3.1.2 Analyzing and evaluating time-dependent Young Modulus E(t) of two groups of concrete (Group Regular concrete; Group - Steel fiber reinforced concrete) According to the experimental results of time-dependent Young modulus of regular concrete and steel fiber reinforced concrete, proposing the formulas and the experimental coefficients which indicate the relation between the Young modulus E(t) and the Young modulus of 28 days based on the total least-squares method (use the Solver tool in Microft Excel) 𝐸(𝑡) = 𝐸(28) 𝑡 2,24 + (0,92 𝑡) (3.2) Table 3.2 The suggested results of Young Modulus of concrete E(t) (Group - Regular concrete; Group - Steel fiber reinforced concrete) The average value E(t), MPa Standard deviation 28 60 90 180 270 364 (STD) days days days days days days days The suggested results of Young Modulus of concrete E(t) (Group - Regular concrete) M1-ĐX 0.40 25843 32045 33473 33914 34367 34520 34600 3142 M2-ĐX 0.45 23377 28988 30280 30679 31088 31227 31299 2842 M3-ĐX 0.50 20912 25931 27087 27443 27810 27934 27999 2542 The suggested results of Young Modulus of concrete E(t) (Group - Steel fiber reinforced concrete) MS1-ĐX 0.40 26786 33215 34695 35152 35621 35781 35863 3256 MS2-ĐX 0.45 24281 30109 31451 31865 32290 32435 32510 2952 Specimens group Ratio (N/X) MS3-ĐX 0.50 21764 26987 28190 28561 28942 29072 29139 2646 15 Figure 3.3 The experimental results and Figure 3.4 The experimental results and suggested results of Young Modulus of concrete suggested results of Young Modulus of concrete E(t) (Group 1- Regular concrete) E(t) (Group - Steel fiber reinforced concrete) 3.2 Comparison of time-dependent compressive strength Rn(t) and Young Modulus E(t) of two groups of concrete in natural climatic conditions (Group - Regular concrete; Group - Steel fiber reinforced concrete) Table 3.3 The results of compressive strength of concrete Rn(t) between Group - Regular concrete and Group - Steel fiber reinforced concrete 0.40 days 1.059 28 days 1.058 Comparativevalue (kR) 60 90 180 days days days 1.055 1.051 1.048 0.45 0.50 1.063 1.065 1.060 1.062 1.055 1.059 Specimens group Ratio (N/X) RMS1 với RM1 RMS2 với RM2 RMS3 với RM3 1.053 1.055 1.050 1.052 270 days 1.047 364 days 1.046 1.050 1.052 1.047 1.049 Table 3.4 The results of Young Modulus E(t) between Group - Regular concrete and Group - Steel fiber reinforced concrete days 28 days Comparativevalue (kE) 60 90 180 days days days 0.40 0.45 1.038 1.041 1.037 1.039 1.033 1.037 1.030 1.034 1.028 1.031 1.027 1.029 1.025 1.027 0.50 1.042 1.041 1.040 1.036 1.033 1.031 1.030 Specimens group Ratio (N/X) EMS1 với EM1 EMS2 với EM2 EMS3 với EM3 270 days 364 days Figure 3.5 The comparision of compressive Figure 3.6 The comparison of Young Modulus strength of concrete Rn(t) between Group - E(t) between Group - Regular concrete and Regular concrete and Group - Steel fiber Group - Steel fiber reinforced concrete reinforced concrete 16 3.3 Determination of the experimental coefficients which predictthe time-dependent shrinkage strains of concrete (Group - Regular concrete) in standard climatic conditions of Gia Lai according to Russian Standard GOST 24544-81 Table 3.5 Values of experimentalcoefficientscalculated according to GOST 24544-81 of concrete specimens (Group - Regular concrete) Spec M1 M2 M3 𝑋̅ 𝑌̅ 𝑆12 𝑆22 𝑚1,2 𝑟 𝐵 𝐴 107,97 0,2336 9001.32 0.019 12.9791 0.99976 0.0014 0.0779 107,97 0,2090 9001.32 0.018 12.5949 0.99982 0.0014 0.0579 107,97 0,1904 9001.32 0.016 11.9143 0.99966 0.0013 0.0474 𝜀𝑐𝑠 (∞) (x10−6 ) 𝛼𝑛 693.52 714.68 755.51 54.01 41.41 35.85 - The formula for predicting of the shrinkage strains of regular concrete specimens M1 which have ratio of N/X of 0.40: 𝑡 (3.3) 54,01 + 𝑡 - The formula for predicting of the shrinkage strains of regular concrete specimens M2 which have 𝜀𝑐𝑠 (𝑡) = 693,52 10−6 ratio of N/X of 0.45: 𝑡 (3.4) 41,41 + 𝑡 - The formula for predicting of the shrinkage strains of regular concrete specimens M3 which have 𝜀𝑐𝑠 (𝑡) = 714,68 10−6 ratio of N/X of 0.50: 𝜀𝑐𝑠 (𝑡) = 755,51 10−6 𝑡 35,85 + 𝑡 (3.5) Figure 3.7 Experiment and suggested results of Figure 3.8 Experiment and suggested results of time-dependent shrinkage strains of regular time-dependent shrinkage strains of regular concrete specimens M1 concrete specimens M2 Figure 3.9 Experiment and suggested results of time-dependent shrinkage strains of regular concrete specimens M3 17 3.4 Comparison between the suggested prediction and Australian Standard AS 3600 and Forecast model of Russian Concrete Institute Figure 3.10 The shrinkage strain results of suggested prediction and AS 3600 and Forecast model of Russian Concrete Institute 3.5 Evaluation of effect of ratio between water and cement N/X on shrinkage strains of 03 concrete groups in standard climatic conditions of Gia Lai (Group - Regular concrete; Group - Steel fiber reinforced concrete; Group - Reinforced concrete) 3.5.1 Effect of ratio N/X on shrinkage strains of concrete specimens of group Figure 3.11 Time-dependent shrinkage strains of Figure 3.12 Relation between time-dependent concrete specimens of Group - Regular concrete shrinkage strains and mass loss of concrete specimens of Group - Regular concrete 3.5.2 Effect of ratio N/X on shrinkage strains of concrete specimens of group Figure 3.13 Time-dependent shrinkage strains of Figure 3.14 Relation between time-dependent concrete specimens of Group - Steel fiber shrinkage strains and mass loss of concrete reinforced concrete specimens of Group - Steel fiber reinforced concrete 18 3.5.3 Effect of ratio N/X on shrinkage strains of concrete specimens of group Figure 3.15 Time-dependent shrinkage strains of Figure 3.16 Relation between time-dependent concrete specimens of Group - Reinforced shrinkage strains and mass loss of concrete concrete specimens of Group - Reinforced concrete 3.5.4 Evaluating effect of ration N/X on shrinkage strains of concrete (Group - Regular concrete; Group - Steel fiber reinforced concrete; Group - Reinforced concrete) N/X ratio affects to the shrinkage strains of concrete dramatically Increasing the ratio of N/X will increase shrinkage strains of concrete The possibility of crack in concrete structures depending on those strains is high Dehydration of concrete depending on evaporation and hydration of cement is high in the early days after concreting Mass loss of concrete due to dehydration is proportional to shrinkage strain of concrete; Reducing ratio of N/X is one of solutions to reduce the shrinkage strain of concrete This should be considered in the design process of concrete mix 3.6 Shrinkage strains of concrete of Group - Regular concrete, Group - Steel fiber reinforced concrete and Group - Reinforced concrete in standard climatic conditions of Gia Lai Figure 3.17 Time-dependent shrinkage strains of Figure 3.18 Time-dependent shrinkage strains of concrete specimens of Group and Group concrete specimens of Group and Group 3.7 Shrinkage strains of concrete of Group - Regular concrete, Group - Steel fiber reinforced concrete and Group - Reinforced concrete in standard and natural climatic conditions of Gia Lai 3.7.1 Comparison of shrinkage strains of three groups of concrete with the same concrete mix design, different ratio of N/X in standard and natural climatic conditions of Gia Lai 19 Figure 3.19 Time-dependent shrinkage strains of Figure 3.20 Time-dependent shrinkage strains of concrete specimens of Group in standard and concrete specimens of Group in standard and natural climatic conditions of Gia Lai natural climatic conditions of Gia Lai Figure 3.21 Time-dependent shrinkage strains of concrete specimens of Group in standard and natural climatic conditions of Gia Lai 3.7.2 Comparison of shrinkage strains of three groups of concrete with the different concrete mix design, same ratio of N/X in standard and natural climatic conditions of Gia Lai Figure 3.22 Time-dependent shrinkage strains of Figure 3.23 Time-dependent shrinkage strains of concrete specimens of three groups with ratio of concrete specimens of three groups with ratio of N/X of 0.4 in standard and natural climatic N/X of 0.45 in standard and natural climatic conditions of Gia Lai conditions of Gia Lai 20 Figure 3.24 Time-dependent shrinkage strains of concrete specimens of three groups with ratio of N/X of 0.50 in standard and natural climatic conditions of Gia Lai 3.8 Shrinkage strains of concrete of Group - Regular concrete with same concrete mix design, same ratio of N/X in standard and natural climatic conditions of Gia Lai Table 3.6 The results of Shrinkage strains of concrete of Group - Regular concrete with same concrete mix design, same ratio of N/X in natural climatic conditions and standard of Gia Lai 14 21 28 N/X = 0.40 M1-ĐKTN/M1-ĐKC 0.00 2.32 1.89 1.87 1.86 1.86 1.86 1.86 1.85 1.60 N/X = 0.45 M2-ĐKTN/M2-ĐKC 0.00 2.33 1.91 1.90 1.88 1.87 1.86 1.85 1.86 1.55 N/X = 0.50 M3-ĐKTN/M3-ĐKC 0.00 2.36 1.93 1.92 1.89 1.88 1.86 1.86 1.85 1.52 35 42 1.41 1.30 1.40 1.28 1.38 1.25 49 56 1.20 1.15 1.15 1.10 1.14 1.09 63 70 77 84 91 98 105 112 119 126 1.12 1.13 1.12 1.12 1.12 1.10 1.09 1.07 1.11 1.10 1.14 1.13 1.13 1.13 1.11 1.11 1.10 1.07 1.11 1.11 1.12 1.12 1.12 1.12 1.10 1.10 1.11 1.09 1.11 1.11 133 1.08 1.09 1.09 Date 21 140 147 154 168 182 196 224 252 280 N/X = 0.40 M1-ĐKTN/M1-ĐKC 1.09 1.10 1.07 1.10 1.10 1.10 1.08 1.09 1.09 N/X = 0.45 M2-ĐKTN/M2-ĐKC 1.11 1.11 1.09 1.11 1.11 1.11 1.09 1.10 1.10 N/X = 0.50 M3-ĐKTN/M3-ĐKC 1.12 1.11 1.09 1.11 1.11 1.11 1.09 1.11 1.10 322 364 1.08 1.09 1.07 1.10 1.07 1.10 Date 3.9 Shrinkage strains of concrete of Group - Regular concrete, Group - Steel fiber reinforced concrete and Group - Reinforced concrete with same ratio of N/X innatural climatic conditions of Gia Lai Table 3.6 The results of shrinkage strains of concrete of Group - Regular concrete, Group - Steel fiber reinforced concrete and Group - Reinforced concrete with same ratio of N/X in natural climatic conditions of Gia Lai 14 21 28 N/X=0.40 M1/ MS1 0.00 1.34 1.15 1.16 1.16 1.17 1.18 1.19 1.21 1.22 N/X=0.45 M2 / MS2 0.00 1.33 1.15 1.15 1.15 1.17 1.18 1.18 1.20 1.21 N/X=0.50 M3 / MS3 0.00 1.30 1.14 1.14 1.15 1.16 1.16 1.18 1.19 1.20 N/X=0.40 M1/ MT1 0.00 1.57 1.30 1.35 1.37 1.38 1.38 1.39 1.40 1.43 N/X=0.45 M2 / MT2 0.00 1.54 1.30 1.34 1.36 1.37 1.38 1.39 1.40 1.42 N/X=0.50 M3 / MT3 0.00 1.51 1.29 1.33 1.35 1.36 1.35 1.38 1.39 1.40 35 42 49 56 63 70 77 84 1.24 1.25 1.24 1.24 1.21 1.21 1.21 1.21 1.23 1.22 1.21 1.21 1.19 1.18 1.18 1.19 1.21 1.17 1.17 1.19 1.17 1.17 1.16 1.16 1.44 1.46 1.45 1.47 1.49 1.46 1.47 1.48 1.45 1.44 1.44 1.45 1.47 1.46 1.45 1.44 1.41 1.43 1.44 1.42 1.41 1.42 1.41 1.38 91 98 1.26 1.18 1.20 1.16 1.17 1.14 1.50 1.46 1.48 1.40 1.41 1.35 105 112 1.14 1.17 1.14 1.16 1.14 1.14 1.39 1.44 1.37 1.39 1.34 1.35 Date 22 119 126 133 140 147 154 168 182 196 N/X=0.40 M1/ MS1 1.14 1.14 1.15 1.14 1.12 1.11 1.11 1.10 1.11 N/X=0.45 M2 / MS2 1.13 1.13 1.13 1.12 1.11 1.12 1.10 1.09 1.10 N/X=0.50 M3 / MS3 1.12 1.11 1.12 1.11 1.10 1.10 1.08 1.07 1.07 N/X=0.40 M1/ MT1 1.34 1.33 1.33 1.31 1.27 1.28 1.24 1.23 1.22 N/X=0.45 M2 / MT2 1.33 1.30 1.30 1.28 1.26 1.26 1.22 1.21 1.21 N/X=0.50 M3 / MT3 1.28 1.27 1.27 1.26 1.24 1.24 1.20 1.17 1.17 224 252 1.13 1.10 1.10 1.10 1.07 1.06 1.24 1.22 1.22 1.18 1.17 1.14 280 322 1.10 1.15 1.09 1.09 1.07 1.06 1.21 1.26 1.18 1.18 1.15 1.14 364 1.09 1.08 1.07 1.20 1.19 1.14 Date 3.10 Evaluating the experimental results of shrinkage strains of regular concrete specimens and steel fiber reinforced concrete specimens by Restrained Ring Test with ratio of N/X of 0.40 Figure 3.25 Time-dependent of strains of steel Figure 3.26 Time-dependent of strains of steel ring in case of regular concrete with ratio of N/X ring in case of steel fiber reinforced concrete of 0.40 with ratio of N/X of 0.40 3.11 Conclusion of Chapter • Based on the experimental data, the parameters of prediction of time-dependent compressive strength and Young modulus of concrete and steel fiber reinforced concrete were determined • Based on the shrinkage strains experimental dataof concretes which have 0.4, 0.45 and 0.5 of ratio between water and cement in concrete mix design, the catalogue of ultimate shrinkage strain cs(∞) and the parameter n depending on the ratio between water and cement was established As a result, the shrinkage strains of regular concrete cs(t) at arbitrary time were proposed used as below: 𝑡 𝜀𝑐𝑠 (𝑡) = 𝜀𝑐𝑠 (∞) 𝛼𝑛 + 𝑡 • Equations of (3.3), (3.4) and (3.5) used the reliable experimental factors, so the results were in high agreement with the results of model of prediction of shrinkage using Australian Standard AS 3600 in tropical climatic zone 23 • The results of shrinkage strains of concrete in standard climatic conditions of Gia Lai are: - Shrinkage strains of concrete depends on climatic conditions and ratio of N/X dramatically - After 21 days of concrete casting, the shrinkage strains of concrete of natural climatic conditions of Gia Lai province are around twice times than that of standard climatic conditions The incremental coefficient of shrinkage strains kmt considering the fluctuation of humidity in natural climatic conditions of Gia Lai is: kmt = 1.86 when t ≤ 21 days kmt =1.10 when t > 21 days - Using steel fiber reinforced concrete with ratio of steel fiber of 40 (kg/m3) decrease the shrinkage strains of concrete of around 1.15 to 1.20 times mainly in 21 first days after casting The efficiency decreases when ratio of N/X increases - Using reinforced concrete with ratio of reinforcement bar of 1.13% decrease the shrinkage strains of concrete of around 1.30 to 1.40 times mainly in 21 first days after casting The efficiency decreases when ratio of N/X increases - After 21 days of casting, effect of steel fiber and reinforcement bar is smaller than the beginning period of casting CONCLUSIONS AND RECOMMENDATIONS Conclusions The summaries of the thesis “An experimental study on shrinkage strains of concrete in standard climatic conditions at Gia Lai” are listed below: The thesis built the experimental data on the shrinkage strain of concrete using local aggregate in climatic conditions of Gia Lai province These data are used in practical design of reinforced concrete structures The shrinkage of concrete in 364 days with several specimens of the ratio between water and cement (N/X) of 0.40, 0.45 and 0.50 in standard climatic conditions of Gia Lai province (temperature of 25±20C and humidity of 75±5%) were measured The results of experiment are used to determine the experimental coefficients which could predict time-dependent shrinkage strains of regular concrete of compressive strength of concrete B22.5 (M300#) in standard climatic conditions of Gia Lai province - With the ratio of N/X of 0.40: 𝜀𝑐𝑠 (𝑡) = 693,52 10−6 𝑡 54,01 + 𝑡 - With the ratio of N/X of 0.45: 𝜀𝑐𝑠 (𝑡) = 714,68 10−6 𝑡 41,41 + 𝑡 - With the ratio of N/X of 0.50: 𝑡 35,85 + 𝑡 The shrinkage strains of regular concrete in standard and natural climatic conditions at Gia Lai 𝜀𝑐𝑠 (𝑡) = 755,51 10−6 were compared Based on the experimental results, after 21 days of concrete casting, the shrinkage strains of concrete of natural climatic conditions-dry season of Gia Lai province are around twice times than that of 24 standard climatic conditions The incremental shrinkage strains coefficient kmt considering the change of humidity of natural climatic conditions-dry season comparing with standard climatic conditions is: kmt =1.10 when t > 21 days kmt =1.10 when t > 21 days These results are important to propose the effective solutions restricting shrinkage strains of concrete in the first period after casting The shrinkage strains of steel fiber concrete and reinforced concrete were determined The results indicated that the steel fiber and reinforcement bar in concrete reduced the shrinkage strains: - Using steel fiber reinforced concrete with ratio of steel fiber of 40 (kg/m 3) decrease the shrinkage strains of concrete of around 1.15 to 1.20 times mainly in 21 first days after casting The efficiency decreases when ratio of N/X increases - Using reinforced concrete with ratio of reinforcement bar of 1.13% decrease the shrinkage strains of concrete of around 1.30 to 1.40 times mainly in 21 first days after casting The efficiency decreases when ratio of N/X increases - After 21 days of casting, effect of steel fiber and reinforcement bar is smaller than the beginning period of casting - The effect of steel fiber on reducing the cracks due to shrinkage strains of concrete was determined by Restrained Ring Test The steel fiber slowed down the crack formation process and reduced the expansion of crack These results indicated the possibility of using steel fiber in reinforced concrete structures, especially floor of industrial builds, floor of bridges, etc to restrict the crack of concrete due to shrinkage strains - N/X ratio affects to the shrinkage strains of concrete dramatically Increasing the ratio of N/X will increase shrinkage strains of concrete Recommendations The follow works are essential to restrict the shrinkage strains of concrete as well as crack of concrete structures: - The future works focus on researching the solutions of using quality and quantity of the steel bars in concrete which could reduce the crack of concrete depending on shrinkage strains in the periods after casting This research aspect is essential currently because the crack of concrete depending on shrinkage strains is popular - The future works also focus on the experimental study of combination between shrinkage and thermal strains in climatic conditions of Gia Lai province LIST OF PUBLICATIONS IN ACCORDANCE WITH DISSERTATION [1] Tran Ngoc Long, Nguyen Ba Thach, Phan Quang Minh (2016), “Short shrinkage strain along the axis of reinforced concrete column bearing long-term load”, Journal of structural Engineering, ISSN 0866-0762, No (2-2016), pp 54-56 [2] Nguyen Ba Thach (2017), “Experimental study of shrinkage strain of concrete in climate conditions Gia Lai”, Journal of Construction Technology Structure, ISSN 1859.3194, No (25-2017), pp 35-40 [3] Nguyen Ba Thach, Truong Hoai Chinh (2017), “Experimental study of the effect of fiber and reinforcement on shrinkage of concrete in climatic conditions Gia Lai”, The workshop of Building Science and Technology advanced towards sustainable development, ISBN 1859.3194, No (25-2017), pp 100-103 [4] Nguyen Ba Thach, Truong Hoai Chinh (2018), “Experimental study of the effect of fiber and reinforcement on shrinkage of concrete in climatic conditions Gia Lai”, Journal of structural Engineering, ISSN 0866-8762, No (2-2018), pp 85-88 [5] Nguyen Ba Thach (2018), “Experimental study of the ability to limit concrete cracking due to shrinkage strain by using steel fiber reinforced concrete in Gia Lai climate condition”, Structural Journal and digital construction technology, ISSN 1859.3194, No (28-2018), pp 86-91 [6] Nguyen Ba Thach, Truong Hoai Chinh (2018), “Experimental study of the effect of N/X ratio on shrinkage strain of concrete in Gia Lai climate conditions”, Journal of Science & Technology Danang University, ISSN 1859-1531, No (11.132-2018), b 1, pp 79-82 ... of concrete in standard climatic conditions at Gia Lai could be predicted; The experimental study compared the shrinkage strains of concrete in standard and natural climatic conditions at Gia Lai. .. EXPERIMENTAL STUDY ON SHRINKAGE STRAINS OF CONCRETE IN CLIMATIC CONDITIONS AT GIA LAI 2.1 Climatic characteristics at Gia Lai Standard climatic conditions at Gia Lai: According to Pleiku City Metering Station... of concrete Scope of Works: Shrinkage strains of concrete without admixtures in standard climatic conditions of Gia Lai province with specimens: Regular concrete of compressive strength of concrete