The relationship between autogenous shrinkage and pore structure of cement paste with mineral admixtures

In this paper, the combination of fly ash and silica fume, or fly ash and blast furnace slag were used as the composite mineral admixtures in cement paste. The autogenous shrinkage and the pore structure of the hardened cement paste with mineral admixtures were tested, and the relationship of the autogenous shrinkage and pore structure also was discussed. The results indicate that fly ash can reduce the autogenous shrinkage, and silica fume can increase the autogenous shrinkage, and the effect of blast furnace slag is between the two above; although both silica fume and blast furnace slag can weaken the porosity and the mean diameter of cement paste, and increase the volumetric percentage of pores whose diameter is between 5 and 50 nm and pore specific surface, silica fume is better than blast furnace slag in changing the pore structure. The relationship between the autogenous shrinkage and volumetric percentage of pores whose diameter is between 5 and 50 nm is obviously proportional.     

Lightweight properties and pore structure of foamed material made from sewage sludge ash

Pore structure significantly affects the lightweight characteristics and thermal performance of materials. Therefore, in this study, sewage sludge ash (SSA) was used to make lightweight materials. Physical and chemical properties, and how the mixing proportions affected the foaming behavior were investigated, including the lightweight characteristics and pore structure of the materials produced. The experiments showed that the minimum required cement amount was determined by the compressive strength of the sewage sludge ash foamed material (SSAFM), not its alkali content. The hydration of cement and SSA mainly generated pores with diameters of less than 0.1  μm, but cement added with metallic aluminum powder produced pores with diameters larger than 10  μm. The addition of SSA increased the volume of pores smaller than 10  μm. The thermal conductivity of SSAFM was between 0.084 and 0.102 W/m K. Therefore, SSA could be used as the lightweight filler and heat-insulating material.     

Utilization of beet molasses as a grinding aid in blended cements

This paper investigates the viability of using beet molasses as a grinding aid for blended cements with high volumes of mineral admixtures. Different ratios of beet molasses (0.01–0.05% by weight of cement) were added into a blended cement containing 41% of fly ash and GBFS. The influence of beet molasses on performances of blended cement was studied by comparing with one commercially available, triethanolamine-based grinding aid (TA). The results show that when comparing with the blank cement mixture, the cement containing 0.02–0.03% molasses shows a higher compressive strength at 3 days and 28 days, even exceeding the TA mixture. The improved microstructure of the molasses modified cement paste was also demonstrated by the pore structure and SEM measurements. These improvements are attributed to the better particle size distribution induced by the addition of molasses, indicating the potential application of beet molasses as a good grinding aid.     

The effect of using different polymer and cement based materials in pore filling applications on technical parameters of travertine stone

The usage of marbles as a natural building and facing stone shows a gradually rising trend in civil sector all over the world. Due to natural motion, structure of marbles consists of many cracks and holes during formation of rocks. Cracks and holes in the marbles generally increase the wastage ratio and operating costs during production of marbles. Normally, the color consistency, brightness of the colors, hardness, strength, non-porous smooth surface as a hygienic structure are desired properties in the usage of flooring and facing stones.In this study, application of some pore filling methods in travertine and their effects on technical parameters of the rock structure were experimentally investigated. Although travertine has high porosity and is composed of different sizes of pores in its structure, it has a wide usage area in the construction and facing stone industry. Its processing is very easy and is much cheaper than the other marble types. Two different applications were mainly used for the pore filling process. These methods are polyester filling technique and cement filling technique. The use of cement filling method is widely applied in travertine production. The effects of these methods on the rock structure were analyzed and the most suitable filling technique was determined based on the technical data of rock parameters.In this study, in addition to the effective use of cement as a filler material in a travertine stone, different ratios of polymer admixtures as a Stuff (ST) and Poliacrilamid (PA) were used to evaluate the collapse of the filling material through the pores with optimum setting time. These materials were used as a replacement of the cement and calcite with the ratios of 0.1%, 0.5%, 1.0%, 1.5% and 2.0%. Test samples were prepared in the form of 40 cm × 40 cm × 1.2 cm tiles and different ratios of the mixture of cement, calcite and polymer materials were applied on the rock surface. These samples were analyzed in terms of water absorption, point load index and unit volume weight measurements by using appropriate standards, TS 699 and ISRM. According to test results, it was tried to compare the filled and unfilled material properties and to obtain optimum ST–PA and cement usage ratio with respect to improving polishing quality, physical and technical parameters of rock.     

Effects of calcination temperature of kaolinite clays on the properties of geopolymer cements

The aim of this work is to determine the most convenient calcination temperature of kaolinite clays in view of producing geopolymer cements. In this light, the clay fractions of three kaolin minerals were used. The clay fractions were characterized (chemical and thermal analyses and X-ray diffraction) and then calcined in the temperature range of 450 and 800 °C. The obtained amorphous materials were dissolved in a strongly alkaline solution in order to produce geopolymer cements whose pastes were characterized by determining their setting time, linear shrinkage and compressive strength. Hardened geopolymer cement paste samples were also submitted to X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analyses. The setting time of geopolymer cement pastes produced from the clay fractions calcined at 450 °C was very long (test samples could be handled easily only after 21 days at the ambient atmosphere of the laboratory). For the clay fractions calcined between 500 and 700 °C, the setting time of geopolymer cement pastes reduced with increasing temperature and varied between 130 and 40 min. Above 700 °C, the setting time began to increase. The linear shrinkage of the hardened geopolymer cement paste samples aged between 21 and 28 days attained its lowest value around 700 °C. Above 700 °C, the linear shrinkage began to increase. The compressive strength of the hardened geopolymer cement paste samples was between 11.9 and 36.4 MPa: it increased with samples from the clay fractions calcined between 500 and 700 °C but dropped above 700 °C.It can be concluded that the most convenient temperature for the calcination of kaolinite clays in view of producing geopolymer cements is around 700 °C.     

Performance of limestone cement mortars in a high sulfates environment

With the aim of studying the influence of cement composition on resistance in high sulfates environment, standard mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 35% limestone (CEM II/B-LL – 32.5). The pore size distribution of the cement pastes was measured. The mortars were immersed in a 5% Na₂SO₄ solution at 20 °C for 1.5 years and the caused deterioration was been visually observed at a regular basis. Furthermore, the mortars expansion was being estimated by measuring the change of length. At the end of the experiment the compressive strength of the mortars was measured. The deterioration products of the mortars have been identified by means of X-ray diffraction, optical microscopy and environmental scanning electron microscopy. The limestone cement based mortar presented cracking that started at the age of 6 months and continued throughout the experiment. It also displayed high expansion after 250 days of immersion in a 5% Na₂SO₄ caused, as proved using the analytical techniques, by the formation of gypsum and ettringite. Concluding, the cement with 35% limestone did not perform as well as ordinary Portland cement under the most aggressive laboratory conditions. Hence, it is obvious that the addition of limestone in the cement leads to a totally different behaviour than Portland cement with respect to the resistance in high sulfates environment.     

Factors determining the correlations between high strength concrete properties

The factors that influence the reliability of the correlations between the properties of concretes with water-cement ratios between 0.26 and 0.42, tested at the ages of 7, 14, 28 and 365 days, were investigated. For this purpose, from the strength of correlations point of view; (i) the effect of the closeness of the sensitivities of the properties to the pore structure of cement paste and (ii) the effect of the closeness of dependences of the properties on the compositional factors were investigated. It was found that at the ages of 7 and 14 days, the closeness of dependences of the properties on compositional factors is the most important agent in determining the strength of correlations between them. However, at 28 days and after, the reliability of the correlations is mainly influenced by the closeness of the sensitivities of the properties to the pore structure of cement paste.     

Analysis of strength development in cement-stabilized silty clay from microstructural considerations

This paper analyzes the strength development in cement-stabilized silty clay based on microstructural considerations. A qualitative and quantitative study on the microstructure is carried out using a scanning electron microscope, mercury intrusion pore size distribution measurements, and thermal gravity analysis. Three influential factors in this investigation are water content, curing time, and cement content. Cement stabilization improves the soil structure by increasing inter-cluster cementation bonding and reducing the pore space. As the cement content increases for a given water content, three zones of improvement are observed: active, inert and deterioration zones. The active zone is the most effective for stabilization where the cementitious products increase with cement content and fill the pore space. In the active zone, the effective mixing state is achieved when the water content is 1.2 times the optimum water content. In this state, the strength is the greatest because of the highest quantity of cementitious products. In the short stabilization period, the volume of large pores (larger than 0.1 μm) increases because of the input of coarser particles (unhydrated cement particles) while the volume of small pores (smaller than 0.1 μm) decreases because of the solidification of the cement gel (hydrated cement). With time, the large pores are filled with the cementitious products; thus, the small pore volume increases, and the total pore volume decreases. This causes the strength development over time.     

Effects of fineness of cement on polynaphthalene sulfonate based superplasticizer–cement interaction

The effects of fineness of portland cement procured from six different Turkish cement plants, on superplasticizer/cement interaction were investigated. CEM I 42.5 type portland cements (PC) were ground into different finenesses ranging from 280 to 550 m²/kg Blaine values. The effects of PC fineness on initial fluidity and fluidity loss of superplasticized cement paste were evaluated. It was found that increasing the Blaine fineness of incompatible cement up to a certain level reduced the viscosity of cement pastes but had no marked effect on the yield stress of the paste mixtures. Nevertheless, flow loss and also saturation point at 60 min increased with increasing the cement fineness. In other words, pastes with lower viscosity can be produced by using finer cement and more superplasticizer.     

Effects of water–cement ratio and curing time on the critical pore width of hardened cement paste

Mercury intrusion porosimetry (MIP) test is one of the techniques that have been widely used for analyzing the pore size distribution of hardened cement paste (hcp) and also for the determination of the critical pore width. This study presents the test results of the MIP experiments obtained for three different hcp specimens with the water–cement ratios of 0.26, 0.34, and 0.42 which had been cured for 7, 28, and 365 days under water. Thus, the effects of water–cement ratio and curing time on the critical pore width of hcp were investigated. Test results have shown that, within the limits of the work, and in case of complete hydration, the critical pore width of the hcp seems to be independent of water–cement ratio and is of the order of 25 nm. This value can be considered as the critical pore width of the portland cement gel.     

Effects of limestone replacement ratio on the sulfate resistance of Portland limestone cement mortars exposed to extraordinary high sulfate concentrations

A comparative study has been performed on the sulfate resistance of Portland limestone cement (PLC) mortars exposed to extraordinary high sulfate concentrations (200 g/l). PLCs have been prepared by using two types of clinkers having different C₃S/C₂S ratios and interstitial phase morphologies. Blended cements have been prepared by replacing 5%, 10%, 20% and 40% of clinker with limestone. Cubic (50 × 50 × 50 mm) and prismatic (25 × 25 × 285 mm) cement mortars were prepared. After two months initial water curing, these samples were exposed to three different sulfate solutions (Na₂SO₄ at 20 °C and 5 °C, MgSO₄ at 5 °C). Solutions were not refreshed and pH values of solutions were monitored during the testing stage. The compressive strength and length changes of samples have been monitored for a period of 1 year. Additional microstructural analyses have been conducted by XRD and SEM/EDS studies. Results indicated that in general, limestone replacement ratio and low temperature negatively affect the sulfate resistance of cement mortars. Additionally, clinkers of high C₃S/C₂S ratios with dendritic interstitial phase structure were found to be more prone to sulfate attack in the presence of high amounts of limestone.From the results, it is postulated that in the absence of solution change, extraordinary high sulfate content modified the mechanism of sulfate reactions and formation of related products. At high limestone replacement ratios, XRD and SEM/EDS studies revealed that while ettringite is the main deterioration product for the samples exposed to Na₂SO₄, gypsum and thaumasite formation were dominant products of deterioration in the case of MgSO₄ attack. It can be concluded that, the difference between reaction mechanisms of Na₂SO₄ and MgSO₄ attack to limestone cement mortars strongly depends on the pH change of sulfate solutions.     

Durability of gamma irradiated polymer-impregnated blended cement pastes

This study is focusing on durability of the neat blended cement paste as well as those of the polymer-impregnated paste towards seawater and various concentrations of magnesium sulfate solutions up to 6 months of curing. The neat blended cement paste was prepared by a partial substitution of ordinary Portland cement with 5% of active rice husk ash (RHA). These samples were cured under tap water for 7 days. A similar paste was impregnated with unsaturated polyester resin (UPE) followed by gamma rays ranging from 10 to 50 kGy. The obtained data indicated that the polymer-impregnated specimens higher values of compressive strength than those of the neat blended cement paste. In addition, the polymer-impregnated blended cement specimens irradiated at a dose of 30 kGy and neat blended cement specimens were immersed in seawater and different concentrations of magnesium sulfate solutions namely, 1%, 3% and 5% up to 6 months. The results showed that the polymer-impregnated blended cement (OPC–RHA–UPE) paste irradiated at a dose of 30 kGy has a good resistance towards sulfate and seawater attack as compared to the neat blended cement (OPC–RHA) paste. These results were confirmed by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) studies.     

Effect of palm oil fuel ash fineness on the microstructure of blended cement paste

This paper presents the effect of palm oil fuel ash fineness on the microstructure of blended cement paste. Palm oil fuel ash (POFA) was ground to two different finenesses. Coarse and high fineness palm oil fuel ash, with median particle sizes of 15.6 and 2.1 μm, respectively, were used to replace ordinary Portland cement (OPC) at 0%, 20% and 40% by binder weight. A water to binder (W/B) ratio of 0.35 was used for all blended cement pastes. The amorphous ground palm oil fuel ash was characterized by the Rietveld method. The compressive strength, thermogravimetric analysis and pore size distribution of the blended cement pastes were investigated. The test results indicate that the ground palm oil fuel ash was an amorphous silica material. The compressive strengths of the blended cement pastes containing coarse POFA were as high as that of OPC cement paste. Blended cement paste with high fineness POFA had a higher compressive strength than that with coarse POFA. The blended cement pastes containing 20% of POFA with high fineness had the lowest total porosity. The Ca(OH)₂ contents of blended cement paste containing POFA decreased with increasing replacement of POFA and were lower than those of the OPC cement paste. In addition, the POFA fineness had an effect on the reduction rate of Ca(OH)₂. Furthermore, the critical pore size and average pore size of blended cement paste containing POFA were lower than those of the OPC cement paste. The incorporation of high fineness POFA decreased the critical pore size and the average pore size of blended cement paste as compared to that with coarse POFA.     

Effect of micro-silica loading on the mechanical and acoustic properties of cement pastes

This study aimed at investigating the role of ultra fine sand (UFS) in enhancing the mechanical and acoustic properties of cementitious pastes. The microstructural origin of these properties was also identified and compared to the conventional materials. The maximum particle size of the UFS used was 100 μm (100% passing) while 50% of the UFS had less than 20 μm in diameter. Ordinary Portland cement (OPC) was partially substituted by UFS at 1%, 2%, 3%, 4%, 5%, 7.5% and 10% by weight of binder. The blended compounds were prepared using the standard water of consistency. Test samples with dimension of 20 × 20 × 20 mm and 40 × 40 × 160 mm were cast for compression and bending strengths tests, respectively. Circular samples with diameters of about 100 and 29 mm and average thickness of about 30 mm were used for sound absorption tests. All samples were kept in molds for 24 h, and then de-molded and allowed to cure in water for 28 days. The specimens were dried at a temperature of 105 °C for 24 h in an oven before testing. It was found that as the loading of UFS increases both the compressive and bending strength increase up to about 5% UFS loading, then a decrease in these properties was observed. This can be attributed to the pozzolanic effect of UFS resulting in enhancing the chemical reaction between free lime in cement and silica producing more hydration products that makes the paste more homogeneous and dense. In addition, the dispersed UFS has improved the filling effect allowing denser packing of the paste. These dense microstructural features were captured by scanning electron microscope (SEM) examination of the 5% UFS modified compound. The results also showed that, the sound absorption and noise reduction coefficient (NRC) for modified cement paste decreases with the increase of UFS up to 5% and this may be due to the decrease in porosity. However, the NRC began to increase at UFS loadings of 7.5% and 10% due to the increase in the porosity of the compounds.     

Influence of soaking and polymerization conditions on the properties of polymer concrete

An experimental investigation was conducted to study the effect of soaking time and polymerization temperature on the mechanical and physical properties of polymer-impregnated concrete. Soaking time was controlled in 4, 8, 12, 16, 20 and 24 h, polymerization temperature was set at 70, 80 and 90 °C for 0.5, 1, 2, 4, 6, 12 and 24 h in impregnation process, respectively. Cylindrical concrete specimens with water/cement ratios of 0.45 and 0.65 were impregnated with methyl methacrylate (MMA) and benzoyl peroxide (BPO) mixtures. The polymer loading increases as immersion time increases until 12 h. Based on compressive strength and surface absorption, optimum polymerization temperature is 70 °C for Mix A (high cement content) and 80 °C for Mix B (low cement content). Polymer impregnation not only increases concrete strength and resistivity but also greatly decreases surface absorption comparing with normal concrete. SEM and MIP observations indicate that the micro-pores and meso-pores of PIC specimens are filled with PMMA and the total pore volume and maximum pore size are reduced significantly.     

Durability design and performance of self-consolidating lightweight concrete

In terms of the durability, the reduction in cement paste is crucial to both volume stability and long-term performance of concrete. The objective of this paper is to compare the performance of lightweight concrete under different w/cm ratio and different cement paste content. The slump and slump flow spread of fresh self-consolidating lightweight concrete (SCLWC) are designed to be within 230–270 and 550–650 mm, respectively. The test results indicate that the 91-day compressive strength of SCLWC is up to 56 MPa when cement content is 386 kg/m³ and water content is 150 kg/m³. If enough cement paste is used, then the less the paste amount and the denser the packing of aggregate, the higher the strength efficiency of cement and the electric resistance, and the lower the chloride ion penetrability capacity of SCLWC.     

Effect of coarse aggregate size and cement paste volume on concrete behavior under high triaxial compression loading

When massive concrete structures (high-rise buildings, tunnels, dams, nuclear power plants, bridges, protection structures, …) are subjected to extreme loadings (aircraft shocks, rock falls, near-field detonations, ballistic impacts, …), the material undergoes triaxial compression loading at a high confinement. In order to reproduce high stress levels with well-controlled loading paths, static triaxial tests are carried out on concrete samples by mean of a very high-capacity triaxial press. It is a well-known fact that the cement paste volume and the coarse aggregate size are two important parameters of concrete formulation. This article focuses on identifying the effect of coarse aggregate size and cement paste volume on concrete behavior under high triaxial compression. This article shows that at low confinement, the concrete strength slightly increases as the coarse aggregate size increases. At high confinement, the coarse aggregate size has a slight influence on concrete deviatoric behavior and a significant influence on concrete strain limit-state. The higher the coarse aggregate size, the lower is the mean stress level corresponding to concrete strain limit-state. Furthermore, this article highlights that at low confinement, the concrete strength significantly increases with an increase in cement paste volume. Increasing confinement tends to reduce cement paste volume effect on concrete strength. At high confinement, contrary to what has been observed in unconfined compression, the cement paste volume has little effects on concrete deviatoric behavior. Otherwise, decreasing cement paste volume increases concrete deformation capacity. At very high confinement levels and at very high deviatoric stress levels, the axial tangent stiffness of concrete increases as the coarse aggregate size or the cement paste volume is reduced.     

Study of the reactivity of cement/metakaolin binders at early age for specific use in steam cured precast concrete

The paper presents the results of a hydration study performed in order to explain the significant increase in compressive strength at one day of age observed on steam cured mortars when 25% by mass of cement was replaced with a metakaolin. Two CEM I 52.5R cements, differing in reactivity, and a metakaolin (MK) were used. By means of XRD and thermal analysis carried out on cement pastes, blended or not with MK, the main results showed that the improvement in strength at one day of age could be explained by the occurrence of a pozzolanic reaction due to MK, thermo-activated by the high curing temperature (55 °C). The pozzolanic reaction was observed through the consumption of calcium hydroxide and an increase in the amount of C–S–H and C–S–A–H hydrated phases. This change in the hydration product nature and amount was more pronounced when MK was combined with the less reactive cement, in agreement with the mechanical results on mortars. These results are of great importance for the concrete industry where the current trend is to decrease the clinker content in cements (1 ton of clinker = 1 ton of CO₂ released). In particular, the interesting mechanical performance at early ages can be helpful for precast concrete manufacturing.     

Utilization of separator bag filter dust for high early strength cement production

This paper presents the feasibility of incorporating ultra-fine particles collected in the separator bag filter during the process of manufacturing cement (SBFC) as an substitution material for cement. Approximately 2.5% of SBFC is produced during OPC manufacturing process. Also, the average size of SBFC particles is about 5 μm, the average size of OPC particles is about 14 μm. This method does not require additional processes needed in the existing processes to manufacture high early strength cement such as modifying mineral components and adjusting the firing temperature. Moreover, it can also solve the issue of efficiency decrease resulted from the increase of the grinding time applied in the existing process of manufacturing microcement. In order to investigate the characteristic properties of this cement mixture, cement blends have been produced by using different amounts of SBFC. While the blaine value of 100% SBFC was significantly higher (6953 cm²/g) than that of Ordinary Portland Cement (OPC), its chemical composition showed no significant difference. Cement paste, mortar mixtures have been prepared by using cement blends incorporating 0, 50 and 100% SBFC by weight. Flowability, setting time and compressive strength tests has been performed. Test results showed that substitution of SBFC negatively affect the flowability of cement paste and mortar mixtures. Moreover, setting times shortened, compressive and flexural strength values increased by the substitution of SBFC. Finally, microstructure analysis of cement paste samples showed that incorporation of SBFC reduced the internal porosity by 9% as determined by the proposed method. The internal porosity of paste was measured by mercury intrusion porosimetry (MIP). The compressive strength and bending strength of mortar were higher in the order of 100, 50 and 0% SBFC mixed.     

Combined effect of mineral admixtures with superplasticizers on the fluidity of the blended cement paste

The new concrete often incorporates several organic and mineral admixtures which interact with the various constituents of the cements and cause some problems of hardness and workability. In the present study, limestone cement (C1) and pozzolanic cement (C2) were used to make cement paste with two types of superplasticizer; SP1 based on polynaphthalene sulphonate (PNS); and SP2 based on resins melamines (PRM). Marsh cone test was adopted to check the combined effects of the following factors on the fluidity namely the type of cement, the type and the dosage of the superplasticizer, the type and the replacement rate of the mineral admixture and the water–cement ratio (W/C). The results of this work show that limestone cement presents a high fluidity with low loss after 1 h relatively to the pozzolanic cement within the saturation proportioning. Superplasticizer SP1 constitutes an incompatibility case when it is mixed with cement containing high C₃A or alkali content such as C2 cement. Also, limestone powder is found to be the best mineral admixture when it replaces a part of cement, where more fluidity is exhibited caused by the dilution effect.