Microfine Cement Suspensions Research Articles

Use of sand pore-size distribution to predict cement suspension groutability

The investigation reported herein aims toward the development of novel, easy-to-use models based on the pore-size distributions of sands for the groutability prediction of cement suspensions in permeation grouting projects for soil improvement. The models were determined using 367 groutability measurements obtained in this research effort by conducting injection tests into 54 sands with different gradations. The documentation of model performance was based on a large database comprising the results of 604 injection tests conducted by other researchers with ordinary and microfine cement suspensions. Suspension groutability is improved by increasing sand characteristic pore size and suspension water/cement ratio and decreasing cement characteristic grain size and suspension apparent viscosity. The proposed models developed using the Binary Logistic Regression method, exhibit coefficients of multiple determination approximately equal or greater than 0.80 and estimate successfully the outcome of the injection tests collected from other studies at rates ranging from 70% to 76%.

The Effect of Water-to-Cement Ratio on the Penetrability of Cement Grouts: An Experimental Investigation

The use of very fine cement grouts for injection into fine-to-medium sands has been proposed to circumvent problems associated with the permanence and toxicity of chemical grouts and the inability of ordinary cement grouts to permeate soil formations finer than coarse sand. A laboratory investigation was conducted in order to evaluate the penetrability of cement suspensions. Four gradations from CEM I (according to EN 197-1) type of cement were used having nominal maximum grain sizes of 100 μm, 40 μm, 20 μm and 10 μm. The properties of suspensions, with water-to-cement (W/C) ratios of 1:1, 2:1 and 3:1 by weight, were determined in terms of apparent viscosity. Penetrability was evaluated by conducting one-dimensional injections into five different, clean sands using a specially constructed device. Penetrability of cement suspensions increases with increasing water-to-cement (W/C) ratio and cement fineness. Microfine cement suspensions with water-to-cement (W/C) ratios of 2:1 and 3:1 can penetrate into medium-to-fine sands.

Effect of Cement Fineness on the Penetrability of CEM IV/B Based Cement Grouts

Grouting is a common technical method with many applications, e.g. it is used for soil stabilization and strengthening, for reduction for water ingress to underground facilities or of the water loss through a dam foundation, etc. Grouts comprise several constituents, which are combined in many ways depending on the in-situ conditions and the outcome desired. The use of very fine cement grouts for injections into fine-to-medium sands has been proposed to circumvent problems associated with the permanence and toxicity of chemical grouts and the inability of ordinary cement grouts to permeate soil formations finer than coarse sand. A laboratory investigation was conducted in order to evaluate the penetrability of cement suspensions. Four gradations from CEM IV/B (according to EN 197-1) type of cement were used having nominal maximum grain sizes of 100 μm, 40 μm, 20 μm and 10 μm. Suspension properties with water-to-cement (W/C) ratios of 1:1, 2:1 and 3:1 by weight, were determined in terms of apparent viscosity. Penetrability was evaluated by conducting one-dimensional injections into four different, clean sands using a specially constructed device. Penetrability of cement suspensions increases with increasing cement fineness and water-to-cement (W/C) ratio. Microfine cement suspensions with water-to-cement (W/C) ratios of 2:1 and 3:1 can penetrate into medium-to-fine sands.

Investigation on fundamental properties of microfine cement and cement-slag grouts

To ensure excellent rheological behavior, penetrability and mechanical property of microfine cement (MC) grout in the field work, it is essential to obtain and control its property by laboratory tests. In this study, rheological and mechanical properties of six different MC grouts (three portland-based and three slag-blended) and two ordinary Portland cements (ASTM I and III) are measured. MC suspension was prepared at five W/C ratios (1.0, 1.2, 1.5, 2.0 and 3.0) without or with superplasticizer (SP). The properties investigated in this study were: particle size distribution, rheological properties (apparent viscosity, yield stress and plastic viscosity), fresh states (mini-slump, bleed capacity and final setting time) and mechanical properties (early strength development, compressive strength, flexural strength, elasticity modulus, shrinkage/expansion and sand-consolidation strength). The results showed that rheological behaviors and mechanical properties of MC grouts were affected obviously by the W/C ratio, cement fineness, cement type and the addition of SP, etc. All MC suspensions behaved as the Bingham fluids and were stable for W/C=1.0, 1.2 and 1.5. The detrimental effect of finer grain size on viscosity can be negated by using SP. To ensure less leaching, sufficient fluidity and enough penetrability in sand voids or micro cracks, the W/C ratio was recommended as 1.0–2.0. The SP dosages should not be excessive to avoid instability, oversaturation or long-setting.

Effectiveness of Microfine Portland Cement Grouting on the Strength and Permeability of Medium to Fine Sands

The purpose of this research was to investigate the grout properties of microfine Portland cement whose specific surface area was greater than those of the same kind products frequently cited in the relevant literature. In this regard, viscosity, setting time and stability of microfine cement suspensions were initially studied. It was seen that the sedimentation and the setting time increased but the viscosity decreased as the water/cement (W=C) ratio of microfine Portland cement suspensions increased. In addition, the penetrability of microfine Portland cement suspensions with different W=C ratios into various graded medium-to-fine sand specimens prepared at a relative density of 30% was tested under grouting pressures ranging from 0.25 to 0.5MPa. It was observed that the penetrability of cement suspensions into the specimens was successful and increased as the W=C ratio increased. All grouted samples were kept in humidity room at a temperature of 20°C until testing time and subjected to permeability and unconfined compressive strength tests at different time intervals. The unconfined compressive strength decreased as the W=C ratio as well as the fine content of sand increased. Permeability tests conducted on grouted specimens with a period of two months revealed that they were impermeable.

Shear strength of microfine cement grouted sands

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 parameters vary with axial strain, and cohesion attains a maximum value well before failure.

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.

Engineering Properties of Medium-to-Fine Sands Injected with Microfine Cement Grout

This article investigates the penetrability of microfine cement suspensions prepared with Rheocem 900 with and without superplasticizer additive into various graded fine-to-medium sands into which chemical grout permeation is only possible. Initially, the basic rheological properties such as viscosity, setting time, and stability of microfine cement suspensions are studied. In addition, penetration performance of the suspensions into various graded fine to medium sand specimens under different grouting pressures is examined. Finally, the strength and permeability characteristics of various graded fine-to-medium sand specimens permeated with microfine cement suspensions are studied. It is found that a superplasticizer additive greatly increases the grouting performance of microfine cement and reduces the grouting pressure. Moreover, it is seen that the unconfined compressive strengths of sand specimens permeated with a cement grout without additive are slightly less than those of sand specimens permeated with cement grout and superplasticizer additive. Furthermore, permeability tests on specimens permeated with cement grouts with or without a superplasticizer reveals that all specimens are impermeable (k < 1 × 10−7 m/s).

Mechanical Behavior of a Pulverized Fly Ash Grouted Sand

Abstract A laboratory investigation was conducted in order to develop a new grout based on pulverized fly ash. Pulverization of a selected Greek fly ash yielded a gradation with D15 = 1.3 µm, D50 = 6 µm, and D85 = 20 µm and Blaine specific surface approximately equal to 8300 cm2/g. Suspensions of this pulverized fly ash, improved with additives, have comparable properties to ordinary and microfine cement suspensions. Suspensions were injected into clean sands. Permeability, UU, and CU-PP triaxial compression tests were conducted on the grouted specimens. The coefficient of permeability of the sands is reduced by 4 to 7 orders of magnitude. Grouting increases the stiffness and reduces the deformability of the sands. The Mohr-Coulomb failure criterion represents adequately the behavior of the grouted sands, yielding cohesion values ranging from 290 to 450 kPa and angle of internal friction values up to 5° higher than those of the clean sands. The shear strength parameters vary with axial strain, attaining their final values well before failure.

Properties and Performance of a Pulverized Fly Ash Grout

A laboratory investigation was conducted in order to develop a new grout based on fly ash produced in Greece. Ptolemaida fly ash was selected because of its hydraulic properties and was pulverized (Blaine specific surface over 8,300 cm²/gr, \iD\D15\N=1.3 μm, \iD\D50\N=6 μm, and \iD\D85\N=20 μm) in order to improve its groutability and its hydraulic activity. Pulverized fly ash (PFA) suspensions with selected additives have properties comparable to those of ordinary and microfine cement suspensions. Clean sands were injected using two specially constructed devices. Hydraulic conductivity, unconfined compression, and UU and CU-PP triaxial compression tests were conducted on grouted sand specimens. Coarse sands can be grouted effectively with PFA suspensions. Conventional groutability ratios were found to overestimate the groutability of these suspensions. Grouting with PFA suspensions reduces sand hydraulic conductivity by up to seven orders of magnitude and yields unconfined compression strength values up to 3,000 kPa. The Mohr-Coulomb failure criterion represents the behavior of grouted sand with cohesion values ranging from 280 to 450 kPa and angle of internal friction slightly higher than that of the sands.

Development of a pulverized fly ash suspension grout

A Greek lignite fly ash was selected because of its hydraulic properties and was pulverized to produce a specific surface of 8300 cm2/g, and a gradation with D15, D50, and D85 equal to 1.3 μm, 6 μm and 20 μm, respectively. The pulverized fly ash suspension properties were optimized by adding a suitable superplasticizer and a suitable accelerator at optimum dosages. The experimental evaluation of suspension properties included sedimentation tests, viscosity'measurements, rheological properties, setting times and development of strength with time. Groutability and effectiveness were evaluated by injecting selected suspensions into clean sands. Pulverization improves remarkably the behavior of fly ash suspensions. Suspensions with water to solids ratios of 1.5:1 and 2:1 by weight and containing additives, behave as Bingham fluids, have apparent viscosity lower than 70 cP, bleed capacity lower than 5%, initial setting time lower than 24 h, and can be injected into relatively coarse sands. These characteristics are comparable to those obtained for ordinary and microfine cement suspensions, showing that pulverized fly ash suspensions can be used for permeation grouting.

Improving microfine cement suspensions with regard to chemical resistance and groutability (In German) : Tax, M; Kuhling, G; Schulze, B FelsbauV11, N2, 1993, P88–96

Improving microfine cement suspensions with regard to chemical resistance and groutability (In German) : Tax, M; Kuhling, G; Schulze, B FelsbauV11, N2, 1993, P88–96