Betonun hızlandırılmış rötresinin iç yapısıyla ilişkisi
Betonun hızlandırılmış rötresinin iç yapısıyla ilişkisi
Dosyalar
Tarih
1996
Yazarlar
Öztürk, Ali
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Özet
Bu çalışmada betonun hızlandırılmış rötre deneylerindeki davranışının iç yapıyla, beton yaşıyla ve betonun diğer özellikleriyle olan ilişkisi incelenmiştir. Bunun için 3 ayrı granülometride (A8-B8, B8, B8-C8), 3 ayrı çimento dozajında (300, 350, 400 kg/m3 ) ve herbir granülometri ve dozajda 6 farklı su/çimento oranında olmak üzere toplam 54 karışım üretilmiştir. Her bir karışıma ait numuneler 28 ve 90 günlük yaşa ulaşınca bunlar üzerinde hızlandırılmış rötre deneyleri yapılmıştır. Ayrıca bu karışımlardan alman numunelerde, birim ağırlık, küp basınç dayanımı, eğilme dayanımı ve eşdeğer küp basınç dayanımı da ölçülmüştür. Hızlandırılmış rötre üzerinde, granülometri, çimento dozajı, su/çimento oranı, çimento hamuru hacmi ve beton yaşının etkileri incelenmiş, ayrıca ele alınan özelliklerin çimento hamurunun boşluk yapısına duyarlılığı araştırılmıştır. Bundan başka hızlandırılmış rötre değerleriyle çalışmada incelenen diğer özellikler arasındaki bağıntılar hesaplanmıştır. Çalışmadan başlıca şu sonuçlar elde edilmiştir. - Su/çimento oranının yükselmesiyle, hızlandırılmış rötre oranlan, gerek 28, gerekse 90 günlü numunelerde artmıştır. - İnce granülometrilerde hava boşluğu daha fazladır. Bu durumunda aynı dozaj için ince granülometrili betonlarda çimento hamuru hacmi daha büyüktür. Dolayısıyla rötreyi engelleyici etkisi olan agreganın hacmi daha küçük olmaktadır. Bu sebepten agrega granülometrisi inceldikçe hızlandırılmış rötre artmaktadır. - Çimento dozajı arttıkça hızlandırılmış rötrenin arttığı görülmüştür. Bu aslında beklenen bir sonuçtur ve agrega granülometrisinin etkisi gibi çimento hamuru hacminin artışına bağlanabilir. - Çimento hamuru hacmi arttıkça gerek 28, gerekse 90 günlük rötrenin arttığı görülmüştür. - 90 günlük rötreler ile 28 günlük rötreler arasında r^ = 0.7 1663 8 x r28+13.865.10('5) bağıntısı elde edilmiştir. Deneysel sonuçlara ait noktalar bu bağıntı grafiğine yerleştirildiğinde düşük su/çimento oranlarında 90 günlük rötrelerin 28 günlü rötrelerden belirgin derecede büyük olduğu, buna karşı yükse su/çimento oranlarında 28 ve 90 günlük rötrelerin yaklaşık olarak eşit olduğu görülmüştür. Bu durum şöyle açıklanabilir; düşük su/çimento oranlarında hidratasyon hızı daha yavaştır. Yüksek su/çimento oranlarında daha hızlıdır. Yüksek su/çimento oranlarında 28. günde hidratasyon önemli ölçüde tamamlanmakta, bu yüzden 90.gündeki jel miktarı ile 28. gündeki jel miktarı çok farklı olmamakta ve bu iki yaştaki rötre değerleri yaklaşık olarak eşit olmaktadır. Düşük su/çimento oranlarında ise 90. gündeki jel miktarı 28.gündeki jel miktarından belirgin derecede fazla olmakta ve bu yüzden rötre de fazla olmaktadır.
Cracking due to the restrained shrinkage in concrete structures such as highway pavements, slabs, retaining walls, long span bridges and dams can be critical. The importance of shrinkage is largely related to cracking. Drying shrinkage is defined as the time-dependent volume reduction in hardened concrete, as a result of water loss by evaporation. The rate of water loss is related to temperature and relative humidity. The main parameters influencing the drying shrinkage are relative humidity of environment, water/cement ratio of mixture, hydration degree of cement, the elastic properties of the paste and aggregate, size and grading of aggregate admixtures, relative restrainment offered by the aggeregate particles and unhydrated cement, and finally the age of concrete. The comlexity of the subject is such that the effect of the mix design parameters on the equilibrium drying shrinkage of concrete and the fundamental shrinkage parameters of the paste have not been well understood. When the paste fraction in a cencrete specimen looses moisture it shrinks, initially as a result of forces are set up in the solid fraction by capillary forces and subsequently because of the progressive removel of the adsorbed water layers on the pore walls which changes the surface energy of the solid so it contracts. Once the capilarity water has been lost, the withdrawal of adsorbed water takes place which causes shrinkage. Whether a load is subjected or not, cocrete shrinks on drying. Volume changes due to shrinkage is importent because in practice, this movement is partly or wholly restrained and as a result it induces stresses. The main danger generated by shrinkage is the presence of tensile stress induced because, of course, concrete is very weak in tension and sensitive to cracking. Cracks must be avoided or controlled and minimized because they impair the durability and structural integrity, and are also aestheticcaly undesirable. Therefore, it is necessary to take suitable countermeasures to prevent this cracking tendency. Some test methods are proposed in the literature to predict the ultimate drying shrinkage of concrete. In Turkish Standarts two test methods for determining the drying shrinkage of concrete are given. The first, in TS 3322, needs long time periods to predict ultimate drying shrinkage of concrete specimen. The second one, in TS 3453 allows to get results more rapidly. xii The purpose of the present research was to clarify the relationship between these two methods mentioned above. In this study methods of TS 3322 and of TS 3453 are called hydraulic shrinkage and accelerated drying shrinkage respectively. Drying shrinkage is the time-depented volume reduction in hardened concrete, mortar or paste as a result of water loss at constant conditions of temreture and relative humidity. It is generally acknowledged that drying shrinkage of cocrete is a property of the microstructure of the hardened cement paste. The main parameters influencing the drying shrinkage are the shrinkage of the paste, the shrinkage of the aggregate, the relative restrainment offered by the aggregate particles and the unhydrated cement, and the elastic properties of the paste and aggregate. The shrinkage values of the paste and aggregate are dependant on the relative humidity (RH) of drying and time. The shrinkage of the paste is also dependant on the water/cement ratio, the degree of hydration, and the admixtures. The magnitude of drying shrinkage depends on the type and composition of cement used and on the water/cement ratio. The greater the cement content, the greater the shrinkage or expansion. Under moist conditions concrete steadily expands at a rate which decreases with time. It is known that concrete can be considered as a three-phase composite material consisting of hardened cement paste, aggregate and the interfacial region between cement paste and aggregate. Mechanical behaviour, especially deformation and farcture of concrete generally exhibit the most important and complex dependence on the structure of cement paste. But the microstructure of cement paste and the mechanical properties of concrete have generally been studied separately in the past years. It is obvious that this traditional approach has limitations and new research concepts must therefore be used. There have been some attemps to apply a material science approach to study the dependence of the mechanical behaviour of concrete on the structure of cement paste. Properties of concrete or intensitive to cement paste pore structure, which have been proposed and a quantification of the degree of sensitivity will be emphasized here. This study is presented in four chapters. In the first chapter, general information about the theme, related literature and the intend of the study are given. The second chapter involves experimental work and procedure of testing.The characteristics of the mortar compositions, the proportions of mortar mixes, and the methods of curing of specimens are also given in this chapter. In addition, the test results, obtained from hardened concrete are listed together with essential explanations and techniques of calculations in the this chapter. The appraisals of test results with charts are presented in the third chapter. The conclusions, obtained from this work are the subject of the fourth chapter. In the experimental work, three different cement contents were seleqted such as C=300 kg/m3, C=350 kg/m3, C=400 kg/m3 and also different water/cement ratios xiii were used for each cement content. KÇ 32,5 cement was used as a cement and different aggregates were used at the production of mortar. All specimens were kept in water at 20 ° C and in with 50 percent relative humidity and 20° C temperature. Six prismatic specimens of 40x40x160 mm were used for each water/cement ratio for acclerated drying shrinkage tests and there cubic specimens of 150 mm were used for each cement/ratio. The drying shrinkage rate of specimens are calculated by the basis of standarts. The explanations of this method used in this study are given below: The following procedure was applied in this method. - Immersing of specimens in water at 20 ° C for 48 hours - Obtaining the initial length reading on the test specimen - Determining the saturated surface-dry weight of the test specimen. - After removing the specimens from the water bath storing them in oven at 50 ° C - At the end of drying period, removing specimens from oven and cooling to 20°C.Following cooling, obtaining specimen-length and weight, and also length of standard reference bar. - Returning test specimens to the drying oven for a second period of drying. The duration for the second, and subsequent drying periods were 48 hours. Following the second period of drying, repeating cooling, length measurements, and weight determinations as specified before. -After a drying period in the oven for 48 hour, cooling in specified environment until reaching the equilibrium is considered to be prevailing condition when the average length change of the test specimen is less than 0.002 %, over a span of 10 days drying, and also when the average weight loss in 48 h drying is less than 0.2 % with respect to the last previously determined weight. Coefficients and degrees of sensivity are introduced to define quantitively the sensitivity of concrete properties to the pore structure of cement paste. The folowing properties were determined in this study: - Coefficient of sensitivity Let Pu be a hardened concrete property and n( a parameter, and let us consider the values taken by PM in a sample large enough to representative of the concrete in relation to the variable. xiv n; [1- (1.06-2.06s)occ/w]w+a by given several values to n;. Suppose that for n^ri;* the highest coefficient of correlation [RO1;)],^ is obtained. By obtaining this it can be thought that the variable used is the best representation of the influence of the pore structure of cement paste on the property. Thus if n;* =1, this means that the volume of capillary pores and the volume capillary pores and the volume of entrapped air effect the property equally. Hence, the property is insensitive to the pore structure of cement paste. If n;* *1, than the volume of pores and their type affect the property, Which is said to be esensitive to the pore structure of cement paste. How far n;* takes a value different from 1 is an indication of the different effects of the two types of pores on the property. According to this, n;* may be called " the coefficient of sensitivity to the pore structure of cement paste " of the property envisaged. - Sensitive and insensitive properties of concrete with respect to pore structure of cement paste. If a specific property of concrete is effected by amount, but not by the type of pores (Whether capillary or entrapped air) in cement paste, this property is said to be in sensitive to the cement paste pore structure; if the property is effected by by both the amount and type of pores it is said to be sensitive to the paste pore structure. - Determination of sensitivity by comparison with unit weight. Generally it is difficult to determine the coefficient of sensivity defined above since a and s are probably not known exactly. But even so its possible to determine the sensitivity of a property to the pore structure of cement paste, by using an approaximate method which will be explained below. Let us call the unit weight of concrete as A, which is measured when the capilary pore are dried out completely. It is obvious that A must be an insensitive property to the cement paste pore structure, because the decrease in unit weight caused by pores is dependent only on their total volume and not on their shapes and dimensions. In this case if we apply the method explained above to the unit weight (A), the result of n;*=l should be obtained, in other words if we take the variable on the horizontal axis as [1- (1.06-2.06s)ac/w]w+a We must obtain the greatest coefficient of correlation. - Type 1 sensitivity degree of property to the pore structure of cement paste. For any ÇPU ) concrete property, let us call k^/k^ (SD1); = Type 1 sensitivity degree of this (Pfo) property. It was mentioned above that Icq is a parameter of centreal tendency of [1- (1.06-2.06s)ox/w] values and k}* is of ri;* [1- (1.06-2.06s)ac/w] values; (n;*) the coefficient of sensitivity, was constant for a certain concrete property. The Type 1 sensitivity degree (SD1); is defined as: (SDl^k^sn. xv Thus it can be seen that (SD1); Type 1 sensitivity degree of a concrete property P^ is approximately equal to n;* sensitivity coefficient of the same propert defined above. - Type 2 sensitivity degree of properties to the pore structure of cement paste. For any P^ property, the Type 2 sensitivity degree (SD2)j is defined as: (SD2)i = R(ki*)/Ri(k0) where R(kj*)= the highest coefficient of correlation when the variation of the concrete property P^ is calculated with respect to (kw+a) by allocating different values to the k parameter. Ri(k0)=the correlation coefficient obtained by allocating the value Icq to parameter k in the same investigation of the P^ concrete property ( kç, gives the maximum correlation coefficient for unit weight). According to this, (SD2); indicates how much the correlation of the Pu property degenerates with respect to the (kw+a) variable when the sensitivity of Pw is not taken account of and P^ is considered as insensitive. - Sensitivity degrees of obtained according to various functions of c/(kw+a). Lineer regression analysis has been done between the variables [ c/(kw+a)] and the properties PM in the form ; Phi=A[c/(kw+a)] + B Where A and B are regression constants. In these calculations the k parameter has been changed by increaments of 0.4; the k value giving the highest coefficient of correlation for unit weight has been called kç, and k value which gives the highes coefficient of correlation for any other P^ property has been called kj*. Using the equation above, kj* values and (SD1), R( k;*), R^) and (SD2); were also calculated. Further calculations used the following more developed functions of [c/(kw+a)]: Pu = A(c+w+a) + B[ c/(kw+a)]+C Pu = A(c+w+a) + B[ c/(kw+a)]+Cm + D m ; being the fineness modulus of aggregate mixture and A, B, C, D being constants. - Comparison of functions used for expressing the properties. - Relations between properties and compositions with highest correlation coefficients.
Cracking due to the restrained shrinkage in concrete structures such as highway pavements, slabs, retaining walls, long span bridges and dams can be critical. The importance of shrinkage is largely related to cracking. Drying shrinkage is defined as the time-dependent volume reduction in hardened concrete, as a result of water loss by evaporation. The rate of water loss is related to temperature and relative humidity. The main parameters influencing the drying shrinkage are relative humidity of environment, water/cement ratio of mixture, hydration degree of cement, the elastic properties of the paste and aggregate, size and grading of aggregate admixtures, relative restrainment offered by the aggeregate particles and unhydrated cement, and finally the age of concrete. The comlexity of the subject is such that the effect of the mix design parameters on the equilibrium drying shrinkage of concrete and the fundamental shrinkage parameters of the paste have not been well understood. When the paste fraction in a cencrete specimen looses moisture it shrinks, initially as a result of forces are set up in the solid fraction by capillary forces and subsequently because of the progressive removel of the adsorbed water layers on the pore walls which changes the surface energy of the solid so it contracts. Once the capilarity water has been lost, the withdrawal of adsorbed water takes place which causes shrinkage. Whether a load is subjected or not, cocrete shrinks on drying. Volume changes due to shrinkage is importent because in practice, this movement is partly or wholly restrained and as a result it induces stresses. The main danger generated by shrinkage is the presence of tensile stress induced because, of course, concrete is very weak in tension and sensitive to cracking. Cracks must be avoided or controlled and minimized because they impair the durability and structural integrity, and are also aestheticcaly undesirable. Therefore, it is necessary to take suitable countermeasures to prevent this cracking tendency. Some test methods are proposed in the literature to predict the ultimate drying shrinkage of concrete. In Turkish Standarts two test methods for determining the drying shrinkage of concrete are given. The first, in TS 3322, needs long time periods to predict ultimate drying shrinkage of concrete specimen. The second one, in TS 3453 allows to get results more rapidly. xii The purpose of the present research was to clarify the relationship between these two methods mentioned above. In this study methods of TS 3322 and of TS 3453 are called hydraulic shrinkage and accelerated drying shrinkage respectively. Drying shrinkage is the time-depented volume reduction in hardened concrete, mortar or paste as a result of water loss at constant conditions of temreture and relative humidity. It is generally acknowledged that drying shrinkage of cocrete is a property of the microstructure of the hardened cement paste. The main parameters influencing the drying shrinkage are the shrinkage of the paste, the shrinkage of the aggregate, the relative restrainment offered by the aggregate particles and the unhydrated cement, and the elastic properties of the paste and aggregate. The shrinkage values of the paste and aggregate are dependant on the relative humidity (RH) of drying and time. The shrinkage of the paste is also dependant on the water/cement ratio, the degree of hydration, and the admixtures. The magnitude of drying shrinkage depends on the type and composition of cement used and on the water/cement ratio. The greater the cement content, the greater the shrinkage or expansion. Under moist conditions concrete steadily expands at a rate which decreases with time. It is known that concrete can be considered as a three-phase composite material consisting of hardened cement paste, aggregate and the interfacial region between cement paste and aggregate. Mechanical behaviour, especially deformation and farcture of concrete generally exhibit the most important and complex dependence on the structure of cement paste. But the microstructure of cement paste and the mechanical properties of concrete have generally been studied separately in the past years. It is obvious that this traditional approach has limitations and new research concepts must therefore be used. There have been some attemps to apply a material science approach to study the dependence of the mechanical behaviour of concrete on the structure of cement paste. Properties of concrete or intensitive to cement paste pore structure, which have been proposed and a quantification of the degree of sensitivity will be emphasized here. This study is presented in four chapters. In the first chapter, general information about the theme, related literature and the intend of the study are given. The second chapter involves experimental work and procedure of testing.The characteristics of the mortar compositions, the proportions of mortar mixes, and the methods of curing of specimens are also given in this chapter. In addition, the test results, obtained from hardened concrete are listed together with essential explanations and techniques of calculations in the this chapter. The appraisals of test results with charts are presented in the third chapter. The conclusions, obtained from this work are the subject of the fourth chapter. In the experimental work, three different cement contents were seleqted such as C=300 kg/m3, C=350 kg/m3, C=400 kg/m3 and also different water/cement ratios xiii were used for each cement content. KÇ 32,5 cement was used as a cement and different aggregates were used at the production of mortar. All specimens were kept in water at 20 ° C and in with 50 percent relative humidity and 20° C temperature. Six prismatic specimens of 40x40x160 mm were used for each water/cement ratio for acclerated drying shrinkage tests and there cubic specimens of 150 mm were used for each cement/ratio. The drying shrinkage rate of specimens are calculated by the basis of standarts. The explanations of this method used in this study are given below: The following procedure was applied in this method. - Immersing of specimens in water at 20 ° C for 48 hours - Obtaining the initial length reading on the test specimen - Determining the saturated surface-dry weight of the test specimen. - After removing the specimens from the water bath storing them in oven at 50 ° C - At the end of drying period, removing specimens from oven and cooling to 20°C.Following cooling, obtaining specimen-length and weight, and also length of standard reference bar. - Returning test specimens to the drying oven for a second period of drying. The duration for the second, and subsequent drying periods were 48 hours. Following the second period of drying, repeating cooling, length measurements, and weight determinations as specified before. -After a drying period in the oven for 48 hour, cooling in specified environment until reaching the equilibrium is considered to be prevailing condition when the average length change of the test specimen is less than 0.002 %, over a span of 10 days drying, and also when the average weight loss in 48 h drying is less than 0.2 % with respect to the last previously determined weight. Coefficients and degrees of sensivity are introduced to define quantitively the sensitivity of concrete properties to the pore structure of cement paste. The folowing properties were determined in this study: - Coefficient of sensitivity Let Pu be a hardened concrete property and n( a parameter, and let us consider the values taken by PM in a sample large enough to representative of the concrete in relation to the variable. xiv n; [1- (1.06-2.06s)occ/w]w+a by given several values to n;. Suppose that for n^ri;* the highest coefficient of correlation [RO1;)],^ is obtained. By obtaining this it can be thought that the variable used is the best representation of the influence of the pore structure of cement paste on the property. Thus if n;* =1, this means that the volume of capillary pores and the volume capillary pores and the volume of entrapped air effect the property equally. Hence, the property is insensitive to the pore structure of cement paste. If n;* *1, than the volume of pores and their type affect the property, Which is said to be esensitive to the pore structure of cement paste. How far n;* takes a value different from 1 is an indication of the different effects of the two types of pores on the property. According to this, n;* may be called " the coefficient of sensitivity to the pore structure of cement paste " of the property envisaged. - Sensitive and insensitive properties of concrete with respect to pore structure of cement paste. If a specific property of concrete is effected by amount, but not by the type of pores (Whether capillary or entrapped air) in cement paste, this property is said to be in sensitive to the cement paste pore structure; if the property is effected by by both the amount and type of pores it is said to be sensitive to the paste pore structure. - Determination of sensitivity by comparison with unit weight. Generally it is difficult to determine the coefficient of sensivity defined above since a and s are probably not known exactly. But even so its possible to determine the sensitivity of a property to the pore structure of cement paste, by using an approaximate method which will be explained below. Let us call the unit weight of concrete as A, which is measured when the capilary pore are dried out completely. It is obvious that A must be an insensitive property to the cement paste pore structure, because the decrease in unit weight caused by pores is dependent only on their total volume and not on their shapes and dimensions. In this case if we apply the method explained above to the unit weight (A), the result of n;*=l should be obtained, in other words if we take the variable on the horizontal axis as [1- (1.06-2.06s)ac/w]w+a We must obtain the greatest coefficient of correlation. - Type 1 sensitivity degree of property to the pore structure of cement paste. For any ÇPU ) concrete property, let us call k^/k^ (SD1); = Type 1 sensitivity degree of this (Pfo) property. It was mentioned above that Icq is a parameter of centreal tendency of [1- (1.06-2.06s)ox/w] values and k}* is of ri;* [1- (1.06-2.06s)ac/w] values; (n;*) the coefficient of sensitivity, was constant for a certain concrete property. The Type 1 sensitivity degree (SD1); is defined as: (SDl^k^sn. xv Thus it can be seen that (SD1); Type 1 sensitivity degree of a concrete property P^ is approximately equal to n;* sensitivity coefficient of the same propert defined above. - Type 2 sensitivity degree of properties to the pore structure of cement paste. For any P^ property, the Type 2 sensitivity degree (SD2)j is defined as: (SD2)i = R(ki*)/Ri(k0) where R(kj*)= the highest coefficient of correlation when the variation of the concrete property P^ is calculated with respect to (kw+a) by allocating different values to the k parameter. Ri(k0)=the correlation coefficient obtained by allocating the value Icq to parameter k in the same investigation of the P^ concrete property ( kç, gives the maximum correlation coefficient for unit weight). According to this, (SD2); indicates how much the correlation of the Pu property degenerates with respect to the (kw+a) variable when the sensitivity of Pw is not taken account of and P^ is considered as insensitive. - Sensitivity degrees of obtained according to various functions of c/(kw+a). Lineer regression analysis has been done between the variables [ c/(kw+a)] and the properties PM in the form ; Phi=A[c/(kw+a)] + B Where A and B are regression constants. In these calculations the k parameter has been changed by increaments of 0.4; the k value giving the highest coefficient of correlation for unit weight has been called kç, and k value which gives the highes coefficient of correlation for any other P^ property has been called kj*. Using the equation above, kj* values and (SD1), R( k;*), R^) and (SD2); were also calculated. Further calculations used the following more developed functions of [c/(kw+a)]: Pu = A(c+w+a) + B[ c/(kw+a)]+C Pu = A(c+w+a) + B[ c/(kw+a)]+Cm + D m ; being the fineness modulus of aggregate mixture and A, B, C, D being constants. - Comparison of functions used for expressing the properties. - Relations between properties and compositions with highest correlation coefficients.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Sosyal Bilimler Enstitüsü, 1997
Anahtar kelimeler
Beton,
Rötreler,
Concrete,
Shrinkages