Integrative Study on the Effect of Internal Curing on Autogenous and Drying Shrinkage of High-Strength Concrete

Han

2016

ACT

Self Cite

In this paper, the effect of internal curing with pre-soaked lightweight aggregate (PSLWA) on shrinkage and interior relative humidity of four series concretes with compressive strength at 28 days around 30MPa, 60MP, 90MPa and 100MPa is investigated. The shrinkage induced cracking performance of concretes is evaluated with concrete-steel composite ring tests. The results show that the development of the internal relative humidity of concrete since casting exhibits first a vapor saturated stage (RH=100%, stage I), followed by gradually reducing stage (RH<100%, stage II). Under sealing, internal relative humidity at the center of the specimen for a given age is obviously decreased with increase of concrete strength. Under drying, similar internal relative humidity value is observed at 28 days for all concretes without internal curing. As PSLWA was added, the reduction rate on interior humidity in stage II is significantly decreased. But the efficiency on internal humidity rising is greatly influenced by concrete strength. The autogenous shrinkage is increased with increase of concrete strength. The drying shrinkage is decreased with increase of concrete strength. The total shrinkage of concrete is increased with increase of concrete strength. As PSLWA was added, the shrinkage reduction in both autogenous and drying shrinkages is obviously in high strength concretes, such as 90MPa and 100MPa concretes. The shrinkage reduction of internal curing on relatively low strength concrete, such 30MPa and 60MPa concrete is not obvious. Internal curing with PSLWA can greatly improve the shrinkage induced cracking performance. All concrete rings without internal curing are cracked under drying. The compressive strain in the steel ring at the concrete ring cracking is about 75 to 101μm/m. By contrast, the stable compressive strain at the inner steel ring for the concretes with internal curing becomes 10 to 40μm/m and no visible cracks were found on the specimens.

Section: Development Of Shrinkage and Internal Relative Humiditymentioning

confidence: 92%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evaluation of Shrinkage Induced Cracking in Concrete with Impact of Internal Curing and Water to Cement Ratio

Han

2016

ACT

Self Cite

Advances in Cement Research

“…During the expansion period (III), the autogenous shrinkage curve decreases. This may be due to internal temperature variations causing slight expansion (Zhang et al, 2013). Moreover, in this period, large quantities of needle-like products of ettringite crystals are quite likely to be not parallel to each other.…”

Section: Periods Based On Autogenous Shrinkage and Its Relationship Wmentioning

confidence: 96%

Relations among electrical resistivity, chemical and autogenous shrinkage of cement pastes

Zuo¹,

Wei²

2015

Electrical resistivity, chemical shrinkage and autogenous shrinkage were measured for cement pastes with different water to binder (w/b) ratios (0 . 30, 0 . 35 and 0 . 40) and fly ash replacements of cement (0%, 30% and 50%). The electrical resistivity, chemical shrinkage and autogenous shrinkage of the pastes decreased with increasing w/b ratio and fly ash content after final setting. The autogenous shrinkage development over time could be divided into a setting period, a rapid growth period, an expansion period and a slow growth period. Based on the test results, the chemical shrinkage and the autogenous shrinkage were linearly correlated to electrical resistivity after hydration for 24 h and 30 h respectively. The linear relationships will help to expand the application of electrical resistivity measurements. The parameter ª, defined as the proportion of autogenous shrinkage to linear chemical shrinkage after the final set, decreased with time due to increasing paste stiffness. This parameter will help researchers quantitatively understand the volume proportion of autogenous shrinkage and empty cavities during hydration.Notation AS(t ) autogenous shrinkage development with time (10 À6 mm/mm) CS(t ) linear chemical shrinkage development with time (10 À6 mm/mm) CS set linear chemical shrinkage before final setting time (10 À6 mm/mm) cs(t ) volumetric chemical shrinkage development with time (mm 3 /mm 3 ) L C loss on ignition of cement (%) L FA loss on ignition of fly ash (%) r fc comprehensive loss on ignition of fly ash cement paste (%) V AS sum volume of autogenous shrinkage (mm 3 ) V CS volume of chemical shrinkage (mm 3 ) V EC volume of empty cavities (mm 3 ) W 105 (t ) sample weight at temperature 1058C at age t (g) W 950 (t ) sample weight at temperature 9508C at age t (g) w nw weight ratio of non-evaporable water per gramme of anhydrous binder materials (%) â fly ash replacement of cement (%) ª proportion of autogenous shrinkage to linear chemical shrinkage after final set AS autogenous shrinkage beginning from final set (10 À6 mm/mm)˜C S linear chemical shrinkage change beginning from final set (10 À6 mm/mm) r electrical resistivity (Ùm) IntroductionSelf-desiccation is a common phenomenon resulting from hydration in high-performance cementitious materials characterised with a low water to cementitious materials ratio. The selfdesiccation of paste in concrete normally leads to a drop in its internal relative humidity; this therefore results in autogenous shrinkage, which increases the risk of cracking in concrete structures especially at early ages (Kim and Lee, 1999;Persson, 1997). In the past decade, it has been frequently reported that early age cracking in concrete deteriorates the durability of concrete structures (Kompen, 1994;Whiting et al., 2000). Figure 1 illustrates autogenous shrinkage caused by self-desiccation. It can be seen that hydration causes the formation of empty cavities and a decrease in internal relative humidity, which creates capillary depression leading to the apparent volume ...

Advances in Materials Science and Engineering

“…Aggregate constitutes approximately 70%-90% of concrete volume. Moreover, aggregate strength directly determines concrete strength; thus, under capillary tension theory, aggregate water absorption is the main factor that affects concrete strength and drying shrinkage [2][3][4][5]. Numerous studies have been conducted on lithology aggregates and the effect of aggregates on concrete strength and drying shrinkage [6][7][8]; reliable physical models have been established according to different theories [9].…”

Section: Introductionmentioning

confidence: 99%

Influence of Aggregate Wettability with Different Lithology Aggregates on Concrete Drying Shrinkage

Guo

Qian

Wang

et al. 2015

The correlation of the wettability of different lithology aggregates and the drying shrinkage of concrete materials is studied, and some influential factors such as wettability and wetting angle are analyzed. A mercury porosimeter is used to measure the porosities of different lithology aggregates accurately, and the pore size ranges that significantly affect the drying shrinkage of different lithology aggregate concretes are confirmed. The pore distribution curve of the different coarse aggregates is also measured through a statistical method, and the contact angle of different coarse aggregates and concrete is calculated according to the linear fitting relationship. Research shows that concrete strength is determined by aggregate strength. Aggregate wettability is not directly correlated with concrete strength, but wettability significantly affects concrete drying shrinkage. In all types’ pores, the greatest impacts on wettability are capillary pores and gel pores, especially for the pores of the size locating 2.5–50 nm and 50–100 nm two ranges.