Andrzej Garbacz

On the characterization of polymer concrete fracture surface

Abstract Fracture surface geometry is often related to material toughness. This approach requires a quantitative description of the fracture surface. The aim of this work was to investigate scale effects on the geometrical features of the fracture surface of polymer concrete (cementless concrete) with different microstructures. Polymer concrete (PC) is a concrete-like composite, in which a resin binder substitutes the cement binder. The fracture surfaces were characterized at different magnifications by: fractal dimension, surface roughness ratio and profile roughness ratio. Relationships between parameters describing the geometry of PC fracture surface were analyzed. The main conclusion is that the geometry of the PC fracture surface depends on the scale of observation.

Modeling of Stress Wave Propagation in Repair Systems Tested with Impact-Echo Method

Abstract Impact-echo method - a stress wave based method - is one of the most promising methods of a repair efficiency assessment. Propagation of stress waves in a repair system is complex phenomenon and depends on acoustic properties of repair material and its thickness as well as a quality of interface. In this work finite element (FE) method was used to simulate stress wave propagation for various models of repair system. Ls-Dyna, an explicit finite element program dedicated for transient dynamics was applied. Several cases of impact-echo test with different parameters of layer system were analyzed. Among considered model parameters were acoustic properties, layer thickness of repair material, concrete roughness, and presence of delamination at the interface. The Fourier transforms and wavelet analysis were applied to characterize signals obtained for particular repair systems. The effect of repair system parameters on wave propagation was discussed.

Effect of Misalignment on Pulloff Test Results: Numerical and Experimental Assessments

The successful application of a concrete repair system is often evaluated through pulloff testing. For such in-place quality control (QC) testing, the inherent risk of misalignment might affect the recorded value and eventually make a difference in the acceptance of the work. The issue of eccentricity in pulloff testing has been ignored in field practice because it is seen as an academic issue. This paper presents the results of a project intended to quantify the effect of misalignment on pulloff tensile strength evaluation and provide a basis for improving QC specifications if necessary. The test program consisted first of an analytical evaluation of the problem through two-dimensional finite element modeling simulations and, in a second phase, in laboratory experiments in which the test variables were the misalignment angle (0, 2, and 4 degrees) and the coring depth (15 and 30 mm [0.6 and 1.2 in.]). It was found that calculations provide a conservative, but realistic, lower bound limit for evaluating the influence of misalignment upon pulloff test results: a 2-degree misalignment can be expect to yield a pulloff strength reduction of 7 to 9%, respectively, for 15 and 30 mm (0.6 and 1.2 in.) coring depths, and the corresponding decrease resulting from a 4-degree misalignment reaches between 13 and 16%. From a practical standpoint, the results generated in this study indicate that when specifying a pulloff strength limit in the field, the value should be increased (probable order of magnitude: 15%) to take into account the potential reduction due to testing misalignment.

Effect of Introducing Recycled Polymer Aggregate on the Properties of C-PC Composites

The subject of this paper is the evaluation of possibility of using the plastic waste fillers as the coarse aggregate of two Concrete-Polymer Composites (C-PC): polymer-cement concrete (PCC) and polymer concrete (PC). The applied fillers were crushed high density polypropylene (HDPP) wastes remaining after grinding plastic elements used in mountings and thermal insulation systems. The substitution of natural mineral coarse aggregate (river gravel) with plastic material was done on the various levels (0 ÷ 40% in case of PCC and 0 ÷ 100% in case of PC). For all composites the density, flexural strength and compressive strength were determined and compared with those for reference composites containing only the river gravel. The results enabled to indicate the levels of possible substitution of the natural aggregate, the non-renewable resource, with waste material, so that the properties of C-PC remain at the satisfactory level.

UIR-Scanner Potential to Defect Detection in Concrete

In the research three NDT methods: indirect Ultrasonic Pulse Velocity, Impact-Echo (IE) and Ground Penetrating Radar (GPR) were used for investigation of concrete slabs with well-defined reinforcement and artificial defects. The obtained results shows the big potential of combination of UPE, IE and GPR methods for detection of wide range of defects in concrete structures. These methods were implemented for UIR scanner development – NDT system which accelerate assessment of concrete structure. Moreover, when the result of one method is not clear and individually the method seems to be not effective, the data from the other one allows for proper interpretation of concrete integrity.

Mortars with phase change materials - Part II: Durability evaluation

The industry of construction is responsible for the high consumption of raw materials, energy and waste production. As such, it becomes imperative to develop and study new constructive solutions with greater sustainable value. The mortars with incorporation of phase change materials (PCM) have the ability to regulate the temperature inside buildings, contributing to the thermal comfort and reducing the use of heating and cooling equipment, using only the energy supplied by the sun. However, the incorporation of phase change materials in mortars modifies its characteristics. The main focus of this study was the durability of mortars with PCM incorporation based in different binders. The binders studied were aerial lime, hydraulic lime, gypsum and cement. For each type of binder, different mortars were developed with different content of PCM. The proportion of PCM studied was 0% and 40% of the mass of the sand. It was possible to observe that the incorporation of PCM in mortars caused differences in properties such as water absorption by capillarity, water absorption by immersion and degradation after freeze-thaw cycles.

Mortars with Phase Change Materials - Part I: Physical and Mechanical Characterization

In a society with a high growth rate and increased standards of comfort arises the need to minimize the currently high energy consumption by taking advantage of renewable energy sources. The mortars with incorporation of phase change materials (PCM) have the ability to regulate the temperature inside buildings, contributing to the thermal comfort and reduction of the use of heating and cooling equipment, using only the energy supplied by the sun. However, the incorporation of phase change materials in mortars modifies its characteristics. The main purpose of this study was the production and characterization in the fresh and hardened state of mortars with incorporation of different contents of PCM in mortars based in different binders. The binders studied were aerial lime, hydraulic lime, gypsum and cement. For each type of binder, different mortars were developed with different content of PCM. The proportion of PCM studied was 0%, 20%, 40% and 60% of the mass of the sand. It was possible to observe that the incorporation of PCM in mortars caused differences in properties such as workability, microstructure, compressive strength, flexural strength and adhesion.

Relation between bond quality and impact-echo frequency spectrum

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond strength evaluation but growing interest in nondestructive techniques (NDT) is recently noted. Impact-echo (IE) is treated as the most promising one for this purpose. The aim of this paper is to analyze an effect of bond quality on stress wave propagation in repair systems. A group of samples has been prepared in order to obtain repair systems of different bond quality. Prior to repair, quality of concrete substrates has been characterized according different techniques: compressive strength, superficial cohesion, surface roughness index and cracking quantification. Than a polymer-modified repair mortar has been applied. After hardening, IE signals have been recorded and pull-off bond strength determined. The relationships between parameters characterizing surface quality, bond strength, IE frequency spectrum and results of wavelet analysis of IE signal have been analyzed. 2 ICPIC 2010 – 13 International Congress on Polymers in Concrete Table 1: Characteristic of tested repair systems Group A Group B Concrete substrate C30 C40 C45 C25 C35 C50 Compressive strength classes C30/37 C40/50 C45/55 C25/30 C35/45 C50/60 Surface preparation PL, SB-D, JH, HD NT, SB-W, SC, LC Sample dimensions 80x60x10 cm 50x50x7cm Repair material PCC (A), Dmax = 2,0mm PCC (B), Dmax = 0,25mm Repair layer thickness 3cm 3cm 2.2 Results of substrate characteristics The quality of substrates was characterized from point of view of their roughness, microcracking and surface tensile strength. The roughness was measured by sand patch test according to EN 1766 resulting Surface Rough Index SRI (Fig.1a). Substrates of Group A can be ranked from polished smooth surface (PL), by dry sandblasted (SB-D) and jack hammered (JH) to very irregular hydrodemolitioned one (HD). In Group B low-pressure waterjetting (LC) has no big influence on profile in comparison to brushed surface (NT), while wet sandblasting (SB-W) and scarification (SC) increase roughness a little. Microcracking of samples of Group A was observed on the cross-section of the 8 cm cores on the near-to-surface layer in the area of 2 cm depth. Density of microcracks was calculated (Fig.1b). It can be concluded, that more aggressive surface preparation technique influence more on microcracking: it was observed two times higher density of microcracks after jack hammering (JH) and hydrodemolition (HD) than after dry sandblasting (SB-D) and polishing (PL). As the aggressiveness of surface treatment of samples of Group B was small, the microcracking was not observed here, although it can be expected a little higher level for scarification. a) 0.0 1.0 2.0 3.0 4.0 5.0 P L SB -D JH H D L C N T SB -W S C surface treatment SR I [m m ] Group A Group B b) Group A 0.00 0.01 0.02 0.03 0.04 0.05 P L SB -D JH H D surface treatment L A [ m m /m m 2 ] Figure 1: Surface Roughness Index, SRI (a) and density of microcracks, LA (b) depending on the method of surface treatment The pull-off test according EN 1542 and ASTM C 1583 04 commonly used for evaluation of bond strength (Fig.2b) was applied for surface tensile strength (fhs) measurement (Fig.2a) including type of failure registration. In case of samples of Group A the concrete quality did not have a major influence on the surface tensile strength after surface treatment as it was for samples of Group B (Fig.3). It can be also observed (Fig.4) that for surfaces jack hammered (Group A) and scarified (Group B), more that 50 % of failures appeared near in the superficial zone (type A1, see Fig.2a). It is probably due to microcracking already mentioned. a) b) A A /B B 15 mm repair material concrete substrate Figure 2: Pull-off for evaluation of surface tensile strength (a) and bond strength (b) A1 A2 A3 15 mm T. Piotrowski, A. Garbacz, A. van der Wiellen, L. Courard, F. Nguyen 3

On Mechanical Characteristics of HFRP Bars with Various Types of Hybridization

The principal objective of this study is to elaborate the reliable properties for hybrid fiber-reinforced polymer (HFRP) bars, which will have the potential to be considered as a competitive alternative to conventional reinforcement for concrete structures. Understanding mechanical performance of HFRP bars with various types of hybridization will allow for more precise design estimations that will balance safety and cost. Numerical modeling of tensile strength test was performed for hybrid carbon/glass fiber-reinforced polymer (HC/GFRP) bars and hybrid carbon/basalt fiber-reinforced polymer (HC/BFRP) bars with the use of finite element analysis (FEA) simulations. The variable parameters were two factors: the bar configuration and volume fraction of fibers. Results indicate that for both HC/GFRP and HC/BFRP bars, the location of carbon fibers in the near-surface region is more appropriate when the volume fraction of carbon fibers is less than volume fraction of glass (or basalt) fibers; otherwise, it is better to locate carbon fibers in the core region. Results of numerical modeling were considered for producing HFRP bars for further experimental investigations.