Improvement in concrete behavior with fly ash, silica-fume and coconut fibres

Robust evaluation of self-healing efficiency in cementitious materials – A review

Measurement of fracture mechanics parameters of concrete containing fly ash thanks to use of Digital Image Correlation (DIC) method

Using digital image correlation to evaluate fatigue behavior of strengthened reinforced concrete beams

Concrete structures with various reinforcements, such as steel bars, composite material tendons, and recently steel plates, are commonly used in civil infrastructures. When an external force overcomes the strength of the bond between the reinforcement and the concrete, bond-slip will occur, resulting in a relative displacement between the reinforcing materials and the concrete. Monitoring bond health plays an important role in guaranteeing structural safety. Recently, researchers have recognized the importance of bond-slip monitoring and performed many related investigations. In this paper, a state-of-the-art review on various smart sensors based on piezoelectric effect and fiber optic technology, as well as corresponding techniques for bond-slip monitoring is presented. Since piezoelectric sensors and fiber-optic sensors are widely used in bond-slip monitoring, their principles and relevant monitoring methods are also introduced in this paper. Particularly, the piezoelectric-based bond-slip monitoring methods including the active sensing method, the electro-mechanical impedance (EMI) method and the passive sensing using acoustic emission (AE) method, and the fiber-optic-based bond-slip detecting approaches including the fiber Bragg grating (FBG) and the distributed fiber optic sensing are highlighted. This paper provides guidance for practical applications and future development of bond-slip monitoring.

https://www.mdpi.com/1424-8220/19/5/1231/pdf

Bond-Slip Monitoring of Concrete Structures Using Smart Sensors-A Review.

Use of digital image correlation technique in full-scale testing of prestressed concrete structures

Prestressed concrete (PC) is the predominant material in highway bridge construction. The use of high-strength concrete has gained wide acceptance in the PC industry. The main target in the highway industry is to increase the durability and the life-span of bridges. Cracking of elements is one aspect which affects durability. Recently, nine 7.62 meter long PC I-beams made with different concrete strength were designed according to a simple, semi-empirical equation developed at the University of Houston (UH) (Laskar et al., ACI Journal 107(3): 330–339, 2010). The UH Method is a function of shear span-to-depth ratio (a/d), concrete strength $$ \sqrt {{f}_{c}' } $$
 , web area $$ b_{w} d $$
 , and amount of transverse steel. Based on testing these girders, the shear cracking strength of girders with different concrete strength and different shear span-to-depth ratio was investigated and compared to the available approaches in current codes such as ACI 318-11 (2011) and AASHTO LRFD Specifications (2010).

/pdf/shear-cracking-of-prestressed-girders-with-high-strength-2ec7tiaa8b.pdf

Shear Cracking of Prestressed Girders with High Strength Concrete

Summary

Prestressed concrete (PC) bridge girders have extra flexural strength due to embedded prestressing tendons. The level of strength depends on the integrity of the concrete-tendon bond in pretensioned PC structures, and this bond can be degraded in the presence of an adequately large mechanical force or over time because of accumulated damage. Bond degradation is characterized by the bond slip of the tendon from the host concrete, and in regards to PC structures, bond slip has only been measured from a global perspective. In this paper, a novel method was developed to measure for the first time the local strain of a prestressing tendon during bond slip. Fiber Bragg grating-based strain sensors were installed directly onto prestressing tendons within a PC girder to provide a local perspective of bond slip as the girder was loaded to failure. Measurement of the local strains in selected tendons, from the beginning of bond slip to the complete loss of the concrete-tendon bond, and the failure of the girder was enabled by the method. Copyright © 2014 John Wiley & Sons, Ltd.

Inference of bond slip in prestressed tendons in concrete bridge girders

Normal strength prestressed concrete I-girders are commonly used as the primary superstructure components in highway bridges. However, shear design guidelines for high strength PC girders are not available in the current structural codes. Recently, ten 7.62 m (25 feet) long girders made with high strength concrete were designed, cast, and tested at the University of Houston (UH) to study the ultimate shear strength and the shear concrete contribution (V
 c) as a function of concrete strength (f′c). A simple semi-empirical set of equations was developed based on the test results to predict the ultimate shear strength of prestressed concrete I-girders. The UH-developed set of equations is a function of concrete strength $(\sqrt {f'_c } )$
 , web area (b
 w
 d), shear span to effective depth ratio (a/d), and percentage of transverse steel (ρ
 t). The proposed UH-Method was found to accurately predict the ultimate shear strength of PC girders with concrete strength up to 117 MPa (17000 psi) ensuring satisfactory ductility. The UH-Method was found to be not as overly conservative as the ACI-318 (2011) code provisions, and also not to overestimate the ultimate shear strength of high strength PC girders as the AASHTO LRFD (2010) code provisions. Moreover, the proposed UH-Method was found fairly accurate and not exceedingly conservative in predicting the concrete contribution to shear for concrete strength up to 117 MPa (17000 psi).

Shear design of high strength concrete prestressed girders

Prestressed Concrete (PC) I-girders are used extensively as the primary superstructure components in Texas highway bridges. A simple semi-empirical equation was developed at the University of Houston (UH) to predict the shear strength of PC I-girders with normal strength concrete through the project Texas Department of Transportation (TxDOT) 0-4759. The UH-developed equation is a function of shear span to effective depth ratio, concrete strength, web area and amount of transverse steel. This report intends to: (1) validate the UH-developed equation for high strength concrete by testing ten 25-ft long full-scale PC I-girders with different concrete strength; and (2) validate the UH-developed equation for different sizes of PC girders and study the possibility of having premature failure due to local failure in end zone. Ten modified Tx28 PC girders were tested for the first objective. The girders were divided into three groups (namely Groups A, C and F) based on the concrete compressive strength. Group A consisted of two girders with a concrete compressive strength of 7000 psi. Group F had four girders with a concrete compressive strength of 13000 psi and Group C included four girders with a compressive strength 16,000 psi. Girders in Group A were designed to have a balanced condition in shear. A pair of girders each belonging to Group F and Group C were designed to have a balanced condition while remaining girders were designed as over-reinforced sections. Each group of the PC girders was tested with different shear span to effective depth ratio so as to get two types of shear failure modes, i.e., web-shear and flexure-shear. The validity of the proposed UH-developed equation was ascertained using the girders test results. UH-developed equation was found to accurately predict the ultimate shear strength of PC girders having concrete strength up to 17,000 psi with enough ductility. Six PC girders of Tx-series with three different sizes were tested for the second objective. The girders were divided into three groups (namely Groups D, E and G) based on the girder depth. The test data shows that the PC girders of the new Tx-series has no cracks under service loads and can reach the maximum shear capacity without having a shear bond failure. Also, these girders’ test results ensured the validity of the UH-developed equations for PC girders with different sizes. Simulation of Concrete Structures (SCS), a finite element program recently developed at UH, was used to predict the shear behavior of the tested girders. Analytical results presented in this report proved the validity of SCS to predict the behavior of PC girders with different concrete strength up to 17,000 psi and with different depth up to 70 inches.

Emad L. Labib

Papers

Use of digital image correlation technique in full-scale testing of prestressed concrete structures

Shear Cracking of Prestressed Girders with High Strength Concrete

Inference of bond slip in prestressed tendons in concrete bridge girders

Shear design of high strength concrete prestressed girders

Shearing in High Strength Concrete Bridge Girders: Technical Report