Effect of Natural and Polypropylene Fibers on early Age Cracking of Mortars

Throughout time, the use of lignocellulosic resources has been implemented in the development of building materials. Among these resources, natural fibers are used as mineral binders reinforcement due to their specific mechanical properties. This experimental investigation focused on effect of flax and hemp fiber reinforcement on the resistance of pozzolanic-based mortars to cracking due to restrained plastic shrinkage. Results were compared with polypropylene fiber reinforcement and with control mortar without fibers. The quantity of fibers added to the mortar mix were respectively 0.25% - 0.5% by mass of binder for polypropylene fibers and 0.5% - 1% by mass of binder for flax and hemp fibers. All fibers have a similar length of 12 mm. The cracking sensitivity was evaluated based on two different methods: the first consists in casting the mortar in a metal mold with stress risers whose criteria are inspired by the ASTM standards. The second consists in pouring the mortar on a brick support. In order to assess the effect of fibers on cracking due to restrained plastic shrinkage, the number of cracks, total crack area and maximum crack width within the first 6 hours after casting were determined using digital image correlation (DIC). Results showed that the flax and hemp fibers were more effective in controlling restrained plastic shrinkage cracking compared to polypropylene fibers. With a natural fiber of 1% by mass of binder, maximum crack width was reduced by at least 70% relative to control mortar based specimens. Natural fibers show great ability to propensity for cracking due to restrained plastic shrinkage; so that, they could be an alternative and ecological solution for polypropylene fibers.

CRACK ANALYSIS OF CFRP REINFORCED CONCRETE BEAMS UNDER SECONDARY LOADING

The paper established the calculation formulas on the average crack spacing and the maximum crack width of CFRP（Carbon Fiber Reinforced Polymer）reinforced concrete beam under the secondary loading. Conversion of CFRP plate area into the reinforcement ratio of the reinforced beam, the calculation formula on the average crack spacing of CFRP reinforced concrete beam under the secondary loading was established. On basis of the calculation formula on the maximum crack width of concrete beam, the calculation formula on the maximum crack width of CFRP reinforced concrete beam under the secondary loading was established. The average crack spacing and the maximum crack width calculated by the formulas in the paper were compared with the test data, it was verified that the formula is correct.

Behavior of Reactive Powder Concrete Beams Exposed to Fire

In this paper, the effect of direct fire flame and steel fiber ratio on some mechanical properties and behavior of the relationship between load and deflection of rectangular reinforced concrete beams under the influence of fire exposure was studied. Concrete specimens were exposed to fire at temperatures ranging from (25- 400 ºC). Three temperature levels of (200, 300, 400 ºC) where chosen for exposure duration of 2.0 hours. After conducting the test, it was found that increasing the proportion of steel fibers in percentages 0.5% to 1% and 1.5% decreases the mid-span deflection at service load by 33%, 50% and 37.5 and increases the ultimate load by 36.36%, 41.6% and 53% respectively. After the beams are exposed to fire, it was noticed that the maximum crack width increases with increasing fire temperature.

A crack theory-based bonded particle model for rock particles considering size effect on crushing strength

Particle breakage shows significant effect on the macroscopic behavior of rock materials, and the discrete element method is a powerful tool to investigate the relationship between micro fracture and macro deformation and strength. In this study, the concept of crack is introduced into the bonded particle model (BPM) to simulate the breakage behaviour of rockfill materials, with randomly placed weak bonds representing cracks. Different from traditional BPM, the number, position and strength of the weak bonds are directly related to the number, position and length of cracks. With a reasonable length distribution of cracks, the proposed model can successfully reflect both the crushing strength variation and size effects. A set of crack parameters including the crack density, minimum crack length, maximum crack length and fractal dimension, are suggested. The crushing characteristics of realistic rockfill particles with two typical shapes are simulated quantitatively and verified with test data. It is found that the proposed model with suggested crack parameters can give reasonable prediction on the Weibull's modulus and size effect of rockfill particles.

Modified F configuration in the treatment of Pauwels type III femoral neck fracture: a finite element analysis

Background The optimal treatment of Pauwels type III femoral neck fracture (FNF) in young patients remains a worldwide challenge in orthopedic surgery. Methods Finite element models of four internal fixations were developed to treat Pauwels type III FNF: a: the traditional inverted triangular parallel cannulated screw (PCS) model, b: the F-technique cannulated screw model, c: the modified F-technique cannulated screw model using a fully threaded screw instead of a partially threaded distally, d: the dynamic hip screw coupled with derotational screw (DHS + DS) model. Under the same conditions, finite element analyses were carried out to compare the displacement and von Mises stress distribution of four internal fixations and femurs, the maximum crack distances of the fracture surfaces, Z axis displacements of four models as well as the stress distribution in the subtrochanteric region. Results The modified F-technique configuration resulted in a more stable fixation as compared to the other three configurations, with respect to the maximum displacement and stress peaks of femur and internal fixations, the maximum crack distances of the fracture surfaces, Z axis displacements of four configurations as well as the stress distribution in the subtrochanteric region. Conclusions Our results suggested that modified F-technique configuration show a better performance in resisting shearing and rotational forces in treating Pauwels type III FNF compared to those using traditional inverted triangular PCS, the F-technique configuration or DHS + DS, providing a new choice for the treatment of FNFs.

Analysis of Crack Width Development in Reinforced Concrete Beams

The reliability and durability of reinforced concrete structures depend on the amount of concrete cracking. The risk associated with cracks generates a need for diagnostic methods for the evaluation of reinforced concrete structures. This paper presents the results of a study of 10 single-span reinforced concrete beams to follow the process of crack formation and changes in their width. The beams were loaded to failure with two forces in a monotonic manner with unloading and in a cyclic manner. Continuous observation of the crack formation process was provided by the digital image correlation system. The simplified method for estimating the maximum crack width is proposed. The presented results confirmed the stochastic character of the process of crack formation and development. The maximum crack widths calculated on the basis of the proposed formula were on the safe side in relation to those calculated according to Eurocode 2. It was also confirmed that the distances between cracks do not depend on the loading manner. Hence the density function describing the distribution of distances between cracks can be used to assess the condition of reinforced concrete elements. The research has also shown the suitability of the DIC system (ARAMIS) for testing concrete elements.

Modified F Configuration in the Treatment of Pauwels Type III Femoral Neck Fracture: a Finite Element Analysis

Background: The optimal treatment of Pauwels type III femoral neck fracture in young patients remains a worldwide challenge in orthopedic surgery. Methods: Finite element models of four internal fixations were developed to treat Pauwels type III Femoral neck fracture: a: the traditional inverted triangular cannulated screw model, b: the F-technique cannulated screw model, c: the modified F-technique cannulated screw model using a fully threaded screw instead of a partially threaded distally, d: the dynamic hip screw coupled with anti-rotational screw model. Under the same conditions, finite element analyses were carried out to compare the displacement and von Mises stress distribution of four internal fixations and femurs, the maximum crack distances of the fracture surfaces, Z axis displacements of four models as well as the stress distribution in the subtrochanteric region. Results: The modified F-technique configuration resulted in a more stable fixation as compared to the other three approaches, with respect to the maximum displacement and stress peaks of femur and internal fixations, the maximum crack distances of the fracture surfaces, Z axis displacements of four configurations as well as the stress distribution in the subtrochanteric region.Conclusions: Our results suggested that modified F-technique configuration show a better performance in resisting shearing and rotational forces in treating Pauwels type III femoral neck fractures compared to those using traditional inverted triangular, the F-technique configuration or dynamic hip screw coupled with anti-rotational screw, providing a new choice for the treatment of femoral neck fractures.