Pavel Schmid

Fracture Process in a Fine-Grained Cement-Based Composite Monitored with Nanoindentation and Acoustic Emission

The contribution is devoted to investigation of the fracture process zone (FPZ) in a fine-grained cement-based composite made from hydrated Portland cement. Particularly, experimental investigations and description of the stable crack propagation using fracture mechanics model are conducted. Three-point bending tests on small composite beams with a central edge notch were performed. The damage due to fracture was monitored by means of nanoindentation performed around the macroscopically observable crack. Acoustic emission events were recorded during the three-point bending test and correlated with load–displacement data. The beneficial effect on the fracture resistance of fine-grained mortar specimens compared to plain cement pastes was quantified.

The Effect of the Carbon Nanotubes on the Mechanical Fracture Properties of Alkali Activated Slag Mortars

New nanomaterials such as carbon nanotubes and nanofibres considerably improve performance of current building materials and they can contribute to new application facilities. Alkali activated slag is a material having a great potential to be used in practice. The main drawback of this material is a high level of autogenous and especially drying shrinkage, which causes a deterioration of the mechanical fracture properties. The aim of this paper is introduce the effect of carbon nanotubes admixture on the microstucture and mechanical performance of alkali activated slag mortars. The three-point bending tests of specimens with central edge notch were performed. Method of acoustic emission was used during this testing.

Effect of Curing Temperature on Mechanical and Fracture Parameters of Alkali-Activated Brick Powder Based Composite

The paper describes alkali-activation of the brick body with potassium water glass having the silicate modulus of 1.0. The 28-days compressive strengths, elasticity modulus, effective fracture toughness, effective toughness, and specific fracture energy of the specimens stored at 20, 40 and 60 °C are evaluated. The storage temperature of specimens and the content of the alkaline solution have a significant influence on all mechanical fracture properties of the studied materials.

Effect of Amorphous Silicon Dioxide Amount on the Mechanical Fracture Parameters of Cement Mortars

This paper presents selected results from a study concerning mechanical fracture parameters related to the formation of the solid structure of cement mortars. The tested mixtures were composed of an invariable quantity of cement (type CEM I 42.5 R) and an increasing amount of amorphous SiO2 (marked with a P), or a variable quantity of cement replaced by varied quantities of amorphous SiO2 (marked with an N). It was decided that the consistencies of the fresh mixtures should be identical: to ensure this, the water-cement ratio was increased as necessary. Quantification of the mechanical fracture parameters of the studied composites (fracture toughness, fracture energy, compressive strength, modulus of elasticity) was performed via the evaluation of fracture tests performed on beam specimens with an initial stress concentrator loaded in three-point bending. Subsequently, the results of the experiments in the form of load versus displacement diagrams were processed using the effective crack fracture model and the work of fracture method.

Components of Fracture Response of Steel Fibre Reinforced Concrete Specimens

Records of fracture tests on steel fibre reinforced concrete notched specimens in a three-point bending configuration are evaluated in detail and selected results are discussed in the paper. The values of fracture parameters are determined using work of fracture method and double-K fracture model. Primarily, the role of plain concrete as a matrix in steel fibre reinforced concrete specimens is studied with regard to the recorded fracture response.

Crack Initiation and Length Change in Modified Alkali Activated Slag Mortars

The aim of this paper was to quantify crack initiation and length change of ordinary Portland cement-based mortar and three types of alkali activated slag mortars: reference one that only slag was used as binder, the second one with same amount of slag and with shrinkage reducing admixture in amount 1 % weight of slag and the third one with 5 % weight of slag replaced by fluidized bed combustion fly ash. Czech standard sand consisting of three different fractions (fulfilling requirements of CSN EN 196-1) was used in all mixtures. The sand to binder ratio was 2:1 and water to binder ratio was 0.40 in all mixtures. Curing and length change testing of the specimens were based on ASTM C596-07 and ASTM C490-7. After demolding and three days of water curing mortar prisms were placed in air storage for 24 days. During this period length change (shrinkage) was measured. After that the three point bending test was performed on these specimens at the age of 28 days to obtain the fracture parameters, which was determined via Double-K fracture model. The initiation of cracks during the fracture tests was also monitored by the acoustic emission method. For comparison, specimens cured in water until the age of 28 days were tested in the same manner.

TOUGHENING MECHANISMS IN CONCRETE: INFLUENCE OF AGGREGATE TYPE

ABSTRACT The paper is concentrated to identification of the toughening mechanisms of concrete with different type of aggregates and to development/change of these mechanisms during the first months of curing. Concretes with addition of three types of aggregates — river gravel, lightweight aggregate (Liapor®) and glass “aggregates” — were submitted to fracture tests at the ages of 7, 28 and 90 days. The mortar/matrix was also prepared and tested. The self-curing effect of pre-wetted Liapor aggregates was also studied.