Mechanical properties and cracking resistance are important in concrete structural design, and they affect the long-term performance of structural component. For example, additional strain caused by shrinkage would increase stress; however, higher creep may lead to relaxation and can reduce stress. Higher deformations can lead to higher stresses that could influence deflection, camber, and prestress loss in prestressed concrete elements and affect cracking potential in cast-in-place applications. Comparing with conventional vibrated concrete (CVC), self-consolidating concrete (SCC) generally requires increased amounts of cementitious and fine materials, or a larger volume of paste, and increased dosages of admixtures to achieve high workability and stability. SCC also has smaller maximum size of aggregate and reduced amount of coarse aggregate. These features could affect the strength, shrinkage, and creep behavior of SCC. This session will summarize recent work on the creep and shrinkage behavior of SCC as well as their effects on the mechanical properties and performance in precast and cast-in-place applications.
(1) Explain shrinkage and creep of cast-in-place and precast SCC;
(2) Discuss shrinkage and creep prediction models for SCC including supplementary cementitious materials;
(3) Describe creep behavior of SCC reinforced with hybrid fibers;
(4) Report the time-dependent performance of an in-service SCC girder bridge.
This session has been AIA/ICC approved for 2 CEU/PDH credits.
Shrinkage and Creep of SCC used for Precast, Prestressed Applications
Presented By: Kamal Khayat
Affiliation: Missouri S&T
Description: Proper evaluation of shrinkage is critical for the design of prestressed structural members. An experimental program was undertaken to evaluate autogenous and drying shrinkage of precast, prestressed self-consolidating concrete (SCC). Sixteen SCC with slump flow of 680 ± 20 mm were evaluated. These mixtures were made with 440 to 500 kg/m3 of binder, Type MS cement or HE cement and 20% Class F fly ash, 0.34 to 0.40 w/cm, viscosity-modifying admixture content of 0 to 100 mL/100 kg of binder, and 0.46 to 0.54 sand-to-total aggregate volume ratio. Two high-performance concretes (HPC) with 0.34 and 0.38 w/cm and slump of 150 mm were also investigated. SCC developed 5% to 30% higher drying shrinkage at 300 days than the HPC but similar autogenous shrinkage. Shrinkage was compared to prediction models proposed by AASHTO 2004 and 2007, CEB-FIP 90, GL 2000, and ACI 209. The CEB-FIP 90 and a modified AASHTO 2004 models are found to provide adequate prediction of shrinkage for precast, prestressed SCC.
Evaluating Prediction Models of Creep and Drying Shrinkage of Self-Consolidating Concrete Containing Supplementary Cementitious Materials/Fillers
Presented By: George Morcous
Affiliation: University of Nebraska Lincoln
Description: Supplementary cementitious materials (SCMs) and fillers play an important role in enhancing the mechanical properties and durability of concrete. SCMs and fillers are commonly used in self-consolidating concrete (SCC) mixtures to also enhance their rheological properties. However, these additives could have significant effect on the viscoelastic properties of concrete. Existing models for predicting creep and drying shrinkage of concrete do not consider the effect of SCM/filler on the predicted values. This study evaluates existing creep and drying shrinkage models, including AASHTO LRFD, ACI209, CEB-FIP MC90-99, B3, and GL2000, for SCC mixtures with different SCMs/fillers. Forty SCC mixtures were proportioned for different cast-in-place bridge components and tested for drying shrinkage. A set of eight SCC mixtures with the highest paste content was tested for creep. Shrinkage and creep test results indicated that AASHTO LRFD provides better creep prediction than the other models for SCC with different SCMs/fillers. Although all models underestimate drying shrinkage of SCC with different SCMs/fillers, the GL2000, CEB-FIP MC90-99, and ACI 209 models provide better prediction than AASHTO LRFD and B3 models. Also, SCC mixtures with limestone powder filler exhibited the highest creep, while those with class C fly ash exhibited the highest drying shrinkage.
Development of Shrinkage and Creep Prediction Model for SCC (B4-TW-SCC) by Cloud-Based Analysis Database and Implementation in Bridge Design Software
Presented By: Wen-Cheng Liao
Affiliation: National Taiwan University
Description: At present, the design methodology and formula, particularly in shrinkage and creep, of Self-Compacting Concrete (SCC) projects in Taiwan are identical to those of Vibrated Concrete (VC), but there are differences in the composition and proportion of the materials in various regions, and obvious differences between the VC and SCC in engineering properties. In this study, the test data of shrinkage and creep in Taiwan and abroad were collected following the framework and parameters of the Northwestern University (NU) database to establish cloud-based analysis SCC database. Based on the Model B4-TW shrinkage and creep prediction model modified by Model B4, this study revised the characteristics of SCC and the localization to develop B4-TW-SCC. In B4-TW-SCC, the modification is mainly about the effect of high volume of cementing material weight and high sand ratio, as well as the effect of drying shrinkage changes on the drying creep. It is worth noting that efficiency in data mining and analysis of huge sets of data are significantly improved by analysis database in development of B4-TW-SCC. The creep curve and data point for specific SCC can be further generated on this cloud-based analysis database and directly implemented in common bridge design software for practical application.
Creep Behavior of Self-Consolidating Concrete Reinforced with Hybrid Fibers
Presented By: Hani Nassif
Affiliation: Rutgers University
Description: Self-Consolidating Concrete (SCC) is one of the recent great advances in concrete technology that is gaining increasing popularity in the United States. The use of fibers with SCC to help mitigate the potential shrinkage cracking is becoming more popular in producing Fiber-reinforced Self-Consolidating Concrete (FR-SCC) for various structural applications. However, there is a need to understand the long-term behavior, such as creep and shrinkage, of FR-SCC, in comparison with SCC, under sustained loads. In particular, the effect of using of hybrid fibers as a combination of steel and polypropylene macro and micro-fibers, has not been fully addressed. There is a need to understand and identify how changes in the composition and porosity of FR-SCC, and consequently the elastic modulus, would affect its early age as well as its long-term performance. The main objective of this paper is to examine the accuracy of available prediction models for creep and shrinkage of SCC with and without fibers. The study included an experimental program to compare compression creep of SCC reinforced with hybrid fibers and creep of non-fibrous as well as mono fibrous SCC. Experimental data for creep and shrinkage were also compared to various prediction models. Results show that a combination of micro and macro polypropylene fibers cause the most reduction in shrinkage but also cause the most increase in creep strain compared to non-fiber reinforced self-consolidating concrete. Furthermore, polypropylene fibers of 1.5" length and steel crimped fibers of 1.5" length cause the highest and lowest increase in specific creep, respectively. Finally, among all models that were considered in this study, the Bazant-Baweja B3 Model is the most accurate model in predicting creep behavior for the FR-SCC mixes while CEB90-99 is the most accurate for predicting shrinkage behavior for FR-SCC.
Time-Dependent Performance of In-Service SCC Girder Bridge
Presented By: Samuel Keske
Affiliation: Wiss, Janney, Elstner Associates, Inc.
Description: The presenters evaluated the time-dependent behavior of Alabama’s first in-service bridge with spans constructed entirely with SCC girders, along with companion laboratory specimens, for over 1,000 days after girder fabrication. Matching spans and specimens included conventionally vibrated concrete (VC). This allowed for direct comparison between SCC and VC of equivalent use, as well as comparison between both materials’ performance and expected or specified/designed performance. Time-dependent mechanical properties, cylinder free shrinkage, cylinder compliance, girder camber, and girder prestress losses were evaluated.