A. I. Droudakis

Bio: A. I. Droudakis is an academic researcher from Democritus University of Thrace. The author has contributed to research in topics: Cement & Superplasticizer. The author has an hindex of 3, co-authored 5 publications receiving 91 citations.

Development of microfine cement grouts by pulverizing ordinary cements

Abstract: Three different cements (CEM I, CEM II/B-M and CEM IV/B according to EN 197-1) containing 0%, 23.5% and 38% of pozzolan, respectively, were pulverized to obtain three additional gradations from each cement, with nominal maximum grain sizes of 40, 20 and 10 μm. Cements with the two finer gradations are classified as “microfine” cements. Suspension properties, groutability and effectiveness of all cements were evaluated for water-to-cement ratios (W/C) of 1, 2 and 3 by weight. A superplasticizer was used to optimize rheological properties. The properties and performance of all suspensions tested are affected primarily by W/C ratio and cement fineness. All microfine cement suspensions have acceptable apparent viscosity, behave as Bingham fluids, are stable for W/C = 1, have reasonable setting times for field applications, have mostly predictable groutability and provide satisfactory strength to grouted sands. The finer gradations of II/B-M cement exhibited the best overall behavior and are considered as the most promising compared to similar gradations of the other two cements.

Factors Affecting Engineering Properties of Microfine Cement Grouted Sands

Abstract: An experimental investigation was conducted in order to evaluate the influence of distance from the injection point and of parameters pertinent to the cement, the suspension and the sand on the effectiveness of microfine cement grouts. Three different cement types, each at three different gradations having nominal maximum grain sizes of 100, 20 and 10 μm, were used. Grouting effectiveness was evaluated by injecting suspensions with water to cement (W/C) ratios of 1, 2 and 3, by weight, into five uniform sand fractions with different grain sizes and eight composite sands with different gradations, using a specially constructed apparatus. Unconfined compression and permeability tests were conducted on the resulting grouted sand specimens, after curing for 28 and 90 days. Microfine cement grouted sands obtained unconfined compression strength values of up to 14.9 MPa and permeability coefficients as low as 1.3 × 10−6 cm/s or by up to 5 orders of magnitude lower than those of clean sands. The W/C ratio and the bleed capacity of suspensions as well as the effective grain size and the permeability coefficient of sands are very important parameters, since they affect substantially the grouted sand properties and are correlated satisfactorily with them. The strength and permeability of grouted sands can increase, decrease or remain constant with distance from the injection point depending on the easiness of suspension penetration into the sands. The improvement of grouted sand properties with increasing distance from the injection point is consistent with the observed increase of the cement content of grouted sands.

Shear strength of microfine cement grouted sands

Abstract: Unconsolidated–undrained (single and multi-stage) triaxial compression tests were conducted to evaluate the shear strength of microfine cement grouted sands. Microfine cements of three different types were obtained by pulverising ordinary cements produced in Greece. Multi-stage triaxial compression tests can be used dependably for determination of the shear strength parameters of cement grouted sands. It has been observed that the Mohr–Coulomb failure criterion represents adequately the behaviour of the grouted sands. Grouting with microfine cement suspensions improves the strength of sands significantly, and the improvement is primarily controlled by the water-to-cement (W/C) ratio of the suspensions. The positive effect of microfine cement grouting on the shear strength of sands is mainly the addition of cohesion, which is substantial even at a distance of 1·2 m from the injection point. Grouting with suspension, using W/C = 1 provides the sand with cohesion of about 2·6 MPa. The shear strength paramete...

Triaxial Compression Testing of Microfine Cement Grouted Sands

Abstract: Unconsolidated-undrained (single and multi-stage) and consolidatedundrained triaxial compression tests with pore water pressure measurement were conducted to evaluate the deformability and shear strength parameters of microfine cement grouted sands. The effects of cement type and gradation, grout water-tocement ratio (W/C), test type and distance from injection point were investigated. Grouting with microfine cement suspensions improves significantly the stress-strainstrength behavior of sands, the improvement primarily controlled by the W/C ratio of the suspensions, and is, generally, superior to grouting with ordinary cements. Grouting with a thick or a thin suspension (W/C=1 or 3), respectively, increases the initial tangent modulus of the sands by a factor of 13 and 3.5, reduces the strain at failure of the sand by a factor of 7.5 and 1.5 and provides the sand with cohesion of about 1500 kPa and 350 kPa.

Groutability estimation of grouting processes with cement grouts using Differential Flower Pollination Optimized Support Vector Machine

Abstract: Display OmittedDifferential Flower Pollination-optimized Support Vector Machine for Groutability Prediction (DFP-SVMGP). A soft computing method for groutability estimation is proposed.A hybrid metaheuristic is constructed to optimize the SVM-based model.The effect of evaluation functions on the model performance is studied.Relevant influencing factors in two datasets have been revealed.The new approach attains high prediction accuracy. This research presents a soft computing methodology for groutability estimation of grouting processes that employ cement grouts. The method integrates a hybrid metaheuristic and the Support Vector Machine (SVM) with evolutionary input factor and hyper-parameter selection. The new prediction model is constructed and verified using two datasets of grouting experiments. The contribution of this study to the body of knowledge is multifold. First, the efficacies of the Flower Pollenation Algorithm (FPA) and the Differential Evolution (DE) are combined to establish an integrated metaheuristic approach, named as Differential Flower Pollenation (DFP). The integration of the FPA and the DE aims at harnessing the strength and complementing the disadvantage of each individual optimization algorithm. Second, the DFP is employed to optimize the input factor selection and hyper-parameter tuning processes of the SVM-based groutability prediction model. Third, this study conducts a comparative work to investigate the effects of different evaluation functions on the model performance. Finally, the research findings show that the new integrated framework can help identify a set of relevant groutability influencing factors and deliver superior prediction performance compared with other state-of-the-art approaches.

Development of an injectable grout for concrete repair and strengthening

Abstract: This paper deals with the coupled effect of temperature and silica fume addition on rheological, mechanical behaviour and porosity of grouts based on CEMI 42.5R, proportioned with a polycarboxylate-based high range water reducer. Preliminary tests were conducted to focus on the grout best able to fill a fibrous network since the goal of this study was to develop an optimized grout able to be injected in a mat of steel fibers for concrete strengthening. The grout composition was developed based on criteria for fresh state and hardened state properties. For a CEMI 42.5R based grout different high range water reducer dosages (0%, 0.2%, 0.4%, 0.5%, 0.7%) and silica fume (SF) dosages (0%, 2%, 4%) were tested (as replacement of cement by mass). Rheological measurements were used to investigate the effect of polycarboxylates (PCEs) and SF dosage on grout properties, particularly its workability loss, as the mix was to be injected in a matrix of steel fibers for concrete jacketing. The workability behaviour was characterized by the rheological parameters yield stress and plastic viscosity (for different grout temperatures and resting times), as well as the procedures of mini slump cone and funnel flow time. Then, further development focused only on the best grout compositions. The cement substitution by 2% of SF exhibited the best overall behaviour and was considered as the most promising compared to the others compositions tested. Concerning the fresh state analysis, a significant workability loss was detected if grout temperature increased above 35 °C. Below this temperature the grout presented a self-levelling behaviour and a life time equal to 45 min. In the hardened state, silica fumes increased not only the grout’s porosity but also the grout’s compressive strength at later ages, since the pozzolanic contribution to the compressive strength does not occur until 28 d and beyond.