A model to quantify the influence of fiber reinforcement on plastic shrinkage cracking
In investigating the use of fiber reinforcement as a method to reduce plastic shrinkage cracking in concrete, thirteen different fibers were tested at various fiber volume concentrations. Tests were performed by placing concrete slab specimens in an environment that accelerated evaporation (temperature = 37 ± 2°C, relative humidity = 20 ± 5%, and wind velocity = 31 ± 4 km/hr). The tests were conducted in accordance with ASTM C1579-06. The influence of various types of fibers was quantified using a crack width reduction ratio (CRR) as outlined in ASTM C 1579-06.^ In addition, research was performed to investigate the potential use of two crack width distribution models to describe the test data. The first model was the Modified Weibull Model which is based on previous work (Qi 2003), where three parameters were allowed to vary for each mixture (slope parameter (α), shape parameter (β), and heterogeneity factor, (Pn)). The second model, which was developed in this thesis, was called the Translation Model. As opposed to the Modified Weibull Model, the Translation Model contains only one parameter that depends on fiber characteristics. The Translation Model was compared with the Modified Weibull model and was determined to have a sufficiently good fit for 35 of the 40 investigated cases (with r 2>0.9). The Translation Model is mathematically easier to use and is shown to be a powerful predictor of plastic shrinkage cracking in fiber reinforced concretes. The predictions from the Translation Model are related to characteristics of the fiber geometry. As a result, the Translation Model can be used to estimate the performance of a fiber before testing.^
Jason Weiss, Purdue University.