Drying shrinkage is an inevitable phenomenon that leads to cracks and eventually remarkable volume changes in hardened concrete. In this study, the drying shrinkage strain behavior of roller compacted concrete pavements (RCCPs) in two different curing conditions was investigated. The variables of RCCPs were coarse to fine aggregate (C/F) ratios of 0.7, 1, 1.2 and 1.5 in two cement dosages of 12% and 15%. Vebe tests of the fresh RCCP as well as the compressive, splitting tensile and flexural tensile strengths of the hardened RCCPs were also performed. The test results indicate that by increasing cement content from 12% to 15%, the drying shrinkage strain increased in both cured and non-cured conditions. Generally, the drying shrinkage strain was significantly increased when the C/F ratio was lower than 1.0. It is highly recommended that C/F aggregate ratio is used in the range of 1.0 to 1.2 in the mixture of RCCP.
La retracción por secado es un fenómeno inevitable que produce fisuras y eventualmente cambios de volumen notables en el hormigón endurecido. En este estudio se investigó el comportamiento de la tracción por retracción por secado de pavimentos de hormigón compactado con rodillo (HCR) en dos condiciones de curado diferentes. Las variables consideradas en estos pavimentos HCR fueron la relación entre el árido grueso y el fino (G/F), considerando valores de 0,7, 1, 1,2 y 1,5, y la dosis de cemento, del 12 % y del 15 %. También se realizaron ensayos Vebe del HCR fresco, así como ensayos de resistencia a la compresión, resistencia a la tracción indirecta y de flexión de los HCR endurecidos. Los resultados de los ensayos indican que al aumentar el contenido de cemento del 12% al 15%, la tracción por retracción por secado aumentó tanto en condiciones de curado como de no curado. En general, la tracción por retracción por secado aumentó significativamente cuando la relación G/F era inferior a 1,0. Se recomienda que la relación G/F del árido esté comprendida en el rango de 1,0 a 1,2 en la mezcla de HCR para pavimentos.
Roller compacted concrete pavement (RCCP) provides a sustainable means of pavement construction, which follows the three sustainability pillars: economic, social and environmental (
Drying shrinkage is an inevitable phenomenon that eventually induces cracking in a concrete member. It is affected by many factors such as aggregate, cement, water, ambient conditions (temperature, humidity and wind velocity), curing conditions and geometry (
The principal variables of drying shrinkage in concrete are aggregate volume and water content (
Although there are some studies on the influence of aggregate on the drying shrinkage of concrete, there is a lack of comprehensive studies on the influence of aggregate and coarse to fine aggregate ratio on the drying shrinkage of RCCP. Furthermore, limited data about the behavior of drying shrinkage of RCCP makes it essential to have a comprehensive investigation on it. Therefore, in this study the drying shrinkage of RCCP was investigated at different coarse to fine aggregate ratios. For this purpose, the drying shrinkage of RCCP in the short and long term, based on different coarse to fine aggregate ratios, was determined. In addition, hardened properties such as compressive, splitting tensile, flexural strengths and Vebe time test were investigated.
The grading curve of the combined coarse and fine aggregate was within Portland Cement Association (PCA) standard limits (
Ordinary Portland cement with a 48 MPa compressive strength at 28 days was used. Specific gravity and specific surface area were 3.14 and 3510 cm2/g, respectively.
The mix proportions that are adopted in this research are shown in
Mix ID | Cement | Water (kg/m^{3}) | Coarse aggregate (Kg/m^{3}) | Fine aggregate (Kg/m^{3}) | Coarse to Fine aggregate ratio | 28-day Compressive strength (MPa) | Vebe time (s) | |
---|---|---|---|---|---|---|---|---|
% | Kg/m^{3} | |||||||
12A | 12 % | 269 | 108 | 812 | 1161 | 0.7 | 36 | 22 |
12B | 986 | 986 | 1 | 42 | 25 | |||
12C | 1076 | 897 | 1.2 | 47 | 28 | |||
12D | 1184 | 798 | 1.5 | 47 | 33 | |||
15A | 15 % | 332 | 133 | 776 | 1108 | 0.7 | 42 | 15 |
15B | 942 | 942 | 1 | 50 | 18 | |||
15C | 1028 | 857 | 1.2 | 51 | 20 | |||
15D | 1131 | 754 | 1.5 | 44 | 24 |
The freshly mixed concretes were compacted in cylindrical molds using an electric vibrating hammer according to ASTM C 1435 (
The laboratory testing program was aimed at measuring the properties of RCCP in terms of workability, strengths and drying shrinkage strain. A modified Vebe test was employed to determine the consistency of RCCP. The hardened properties of concretes were measured by compressive strength, splitting tensile strength and flexural tensile strength tests at 28 days. Drying shrinkage strain of RCCP was measured by a demountable mechanical strain gauge (DEMEC).
To measure drying shrinkage strain, six specimens with 100×100×300 mm dimensions for each mix were prepared and then divided into two groups: cured and non-cured. Three non-cured specimens were measured immediately after demolding and three cured specimens were cured in lime-saturated water for 7 days and were measured when taken out from the water. Both groups were measured every day for the first 7 days, and then every 7 days for 90 days according to ASTM C157 (
The compressive strength and splitting tensile strength tests were performed according to ASTM C39 (
According to ASTM C1170 (
The Vebe time and density for all RCCPs are presented in
As can be seen for all RCCPs with two cement dosages, the strengths of compressive, splitting tensile and flexural tensile reached the peak of the strengths at a coarse to fine aggregate ratio of 1.2. The reason could be due to higher pack-density and a more dense structure of RCCP with a coarse to fine aggregate ratio of 1.2.
ASTMC 330-89 specified that the cylinder compressive strength must be at least 17 MPa at 28 days (
The average drying shrinkage strain development of RCCP specimens over 90 days in cured and non-cured conditions was determined. Therefore, the role of the coarse to fine aggregate ratio on the drying shrinkage of RCCPs was compared and investigated in both conditions. Furthermore, the drying shrinkage values were compared with previous studies.
The mix of 12C with 12% cement content and a coarse to fine aggregate ratio of 1.2 showed the lowest drying shrinkage strain, whereas the mix of 15A with 15% cement content and a coarse to fine aggregate ratio of 0.7 exhibited the highest drying shrinkage strain in most of the periods during the 90 days.
The mix of 12C attained the lowest drying shrinkage strain values after 28 days with 215, 260 and 295 microstrain at 28, 56 and 90 days, respectively. However, at the early ages (before 28 days), the drying shrinkage strain of mix 12C was almost 25% higher than 12A (with 12% cement content and C/F ratio of 0.7). The mix of 12A had the lowest drying shrinkage strain at the early ages until 21 days with 98, 135 and 190 microstrain at 7, 14 and 21 days, respectively. As with 12C, similar trends were observed for 12A, 12B, 12D from 28 days up to 90 days, while the shrinkage values for these mixes were 10% higher than mix 12C on average.
Therefore, it can be concluded that mix 12C might have the lowest drying shrinkage strain in the long term. Pittman and Ragan (
Where S_{c} is the shrinkage of concrete, S_{p} is the shrinkage of the cement paste, a is the volume fraction of aggregate and n is a constant depending on the elasticity of aggregate and varies between 1.2 and 1.7.
On the other hand, incrementing the cement dosage from 12% to 15% led to drying shrinkage increment. The mix of 15A (with 15% cement content and C/F of 0.7) attained the highest drying shrinkage among all non-cured RCCPs, while the drying shrinkage values were 288, 335 and 398 microstrain at 28, 56 and 90 days, respectively. Thus, RCCP with 0.7 C/F and 15% ratio would lead to higher drying shrinkage strain. The RCCP mixes of 15B, 15C and 15D had similar trends in most of the periods with an average drying shrinkage of 350 microstrain at 90 days. However, the average drying shrinkage values for the mix of 15B was almost 10% higher than 15C and 15D from 7 to 28 days. Similar to RCCPs with 12% cement content, the drying shrinkage values had a sharp increment up until 56 days, and afterwards the trends were almost constant up until 90 days.
In total, by incrementing the cement dosage from 12% to 15%, the drying shrinkage of RCCPs had almost 20% increment on average. The drying shrinkage strain had a remarkable increment of 12% when the coarse to fine ratio was lower than 1.0 for RCCPs with 15% cement content. However, for RCCPs with 12%, no significant changes were shown. Therefore, it can be concluded that the RCCPs with 15% cement would tend to exhibit higher drying shrinkage. According to Pittman and Ragan (
Jingfu et al. (
As the non-cured condition, the mix of 12C had the lowest and the mix of 15A had the highest drying shrinkage strain in the long term, respectively. The drying shrinkage values for the mix of 12C were 198, 242 and 310 microstrain at 28, 56 and 90 days, respectively; while, it was 302, 378 and 427 for 15A, respectively.
The mix of 12A had the lowest drying shrinkage strain until 20 days with 188 microstrain while after 20 days the shrinkage values had a significant increase up to 90 days and reached a peak of 390 microstrain at 90 days. The trend and values for the mixes of 12B and 12D were very close to each other, and the ultimate drying shrinkage strain was 330 microstrain on average. Thus, the mix of 12C tends to have the least drying shrinkage strain. This might be due to the higher aggregate content, more coarse aggregate than fine aggregate and higher elasticity in this mix, which exhibited as a shrinkage restrainer in RCCP (
On the other hand, RCCPs with 15% cement content had higher drying shrinkage strain. The mix of 15A attained the highest drying shrinkage values during almost every period, and the shrinkage values were 302, 378 and 427 microstrain at 28, 56 and 90 days, respectively. Therefore, the RCCP that has 15% cement content with a coarse to fine ratio of 0.7 would have higher drying shrinkage strain.
For the mixes 15B, 15C and 15D, the shrinkage values were very close to each other, and the ultimate drying shrinkage strain was 335 microstrain on average. Therefore, mix 15A would attain higher drying shrinkage strain. This might be for two major reasons. The first reason is higher usage of fine aggregate content, which led to lower elasticity in concrete and higher drying shrinkage strain (
In total, as with the non-cured condition, the increase of water and cement content showed an increment in drying shrinkage with an average of 6%. This is because of higher paste volume (conversely less aggregate content). Neville (
In conclusion, the average drying shrinkage strain in non-cured and cured conditions were around 330 and 350 microstrain at 90 days, respectively. According to the literature, the drying shrinkage of RCCP is less than PCC with a maximum of 400-500 microstrain (
However, the effect of curing could not be neglected. While curing contributed to attaining lower drying shrinkage at the early ages, for the long term, curing led to higher drying shrinkage strain. Aslam et al. (
In this study, it was found that RCCP with 1.2 C/F ratio and 12% cement content not only achieved the least drying shrinkage strain in both cured and non-cured conditions, but also, with regard to the results for fresh and mechanical properties (section 3.1 & 3.2), the mix of 12C had the appropriate properties. This is in accordance with Hashemi et al. (
However, it is obvious that the other parameters that might affect the drying shrinkage of RCCP need to be investigated comprehensively.
Model name | Equations | Note |
---|---|---|
ACI 209.2 R-08 ( |
ε_{sh}(t-t_{c})= . ε_{shu} |
t-t_{c}: duration of drying α = 1, f = 35 |
Bazant-Baweja B3 ( |
ε_{sh} (t-t_{c})= − ε_{sh∞} k_{h} S(t-t_{c}) ε_{sh∞} = -ε_{s∞} E_{cm607}=1.167 E_{cm28} E_{cm28=} 4734 = E_{cm28} ( τ _{sh=} 0.085t_{c} ^{-0.08} f_{cm28} ^{-0.25} [(2k_{s} (V/S)^{2}] ε_{s∞} = -α_{1} α_{2}(0.019 w^{2.1}f_{cm28} ^{-0.28} + 270) 10^{-6} K_{h} = 1 - h^{3} S(t) = tanh |
V/S: specimen’s volume-surface ratio (21.428 mm) t_{c}: curing age when the drying shrinkage test starts (7 days) f_{cm28}: 28-day cylinder compressive strength α_{1}: cement type constant =1 α_{2}: constant for curing condition (for cured and non-cured condition 1 and 1.2 respectively) f_{cm28}: 28-day compressive strength w: water content h: relative humidity (70%) t-t_{c}: duration of drying |
GL2000 (Gardner 2004) ( |
ε _{sh} (t-t_{c}) = ε _{shu} β(h)β(t-t_{c}) ε _{shu} = 900k()^{1/2}×10^{-6} β(h)= 1 − 1.18 h^{4} β(t-t_{c})=[^{1/2} |
k: cement type function =1 f_{cm28}: 28-day cylinder compressive strength h: relative humidity (70%) t-t_{c}: duration of drying V/S: specimen’s volume-surface ratio (21.428 mm) |
The ultimate drying shrinkage for Bazant-Baweja B3 and GL2000 models is provided by the related equations in
As is clear, in both curing conditions the drying shrinkage strain provided by both ACI 209.2 R-08 and Bazant-Baweja B3 is lower than the measured shrinkage in this study by an average of 46% and 21%, respectively, while the average drying shrinkage strain that is provided by GL2000 in both curing conditions is 50% higher than the measured RCCPs on average. In total, the Bazant-Baweja B3 and GL2000 models had the lowest and highest difference with the measured drying shrinkage, respectively. Furthermore, Bazant-Baweja B3 gave the best prediction for drying shrinkage strain at the early ages with 17% and 19% difference with the measured RCCPs at 7 and 28 days, respectively.
This study was performed to investigate the effect of coarse to fine aggregate ratios on the drying shrinkage of roller compacted concrete pavement (RCCP) by providing eight mix proportions: four different coarse to fine aggregate ratios (0.7, 1, 1.2 and 1.5) and two cement dosages (12% and 15% of total dry solid mass). The drying shrinkage development was monitored in both cured and non-cured conditions, and measurements commenced once the specimens were demolded for up to 90 days. In addition, the fresh and hardened properties of RCCPs were carried out. The study may have resulted in following conclusions:
Increasing the coarse to fine aggregate ratio from 0.7 to 1.5 for RCCPs, which contained 12% and 15% cement content, led to an increment in Vebe time values by 50% and 60%, respectively.
Increasing the coarse to fine aggregate ratio from 0.7 to 1.2 led to increments in the strengths of compressive, splitting tensile and flexural tensile of about 21%, 17% and 19%, respectively. However, by increasing the coarse to fine aggregate ratio from 1.2 to 1.5, those strengths decreased by around 14%, 7% and 9%, respectively.
For both RCCPs with 12% and 15% cement contents, the compressive, splitting tensile and flexural tensile strengths reached the peak of the strengths at a coarse to fine aggregate ratio of 1.2.
In non-cured condition, around 40% of the entire drying shrinkage strain occurred in the first 7 days after drying, while it was around 70% in the first 28 days. In this condition, the highest and lowest drying shrinkage strain was recorded at 90 days with about 400 microstrain (mix 15A) and 300 microstrain (mix 12C), respectively. While, in cured condition, they were recorded as 430 microstrain (mix 15A) and 310 microstrain (mix 12C), respectively.
In both cured and non-cured conditions, the drying shrinkage strain increased by increasing the cement content from 12% to 15%. In addition, a significant increase was monitored in the drying shrinkage strain when a coarse to fine aggregate ratio lower than 1.0 was used. Therefore, it is recommended to use more coarse aggregate than fine aggregate in the RCCP mixtures.
By considering test results of fresh and mechanical properties, it is recommended to use a coarse to fine aggregate ratio in the range of 1.0 to 1.2 in RCCP mixture.
Bazant-Baweja B3 had the best prediction for drying shrinkage strain of RCCPs compared to ACI 209.2 R-08 and GL2000.
This work was supported by the University of Malaya research grant (grant no. RF001F-2018).