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.     

The assessment of porosity and pore size distribution of limestone Portland cement pastes

The cement production industry is one of the most energy and raw materials consuming one. Over the last years a great effort is performed in order to substitute clinker for less energy demanding materials. Nevertheless, construction industry needs durable materials with improved properties. Limestone is being used in blended cements widely. The most important parameter that affects all the properties of cement paste is its pore structure. In this study, four different limestone cements were produced and their pore structure was determined by means of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) cryoporometry. The conclusion of the study was that limestone addition affects the pore structure of the cement paste by increasing linearly the size of capillary pores from 20 nm to 40 nm when the maximum amount (35%) of limestone that is allowed by EN 197-1 is used. On the other hand the threshold diameter decreases exponentially and it is evident that limestone hardened cement pastes have many pores of the same size due to the filling effect that minerals additives have. Furthermore, limestone decreases the size of gel pores which is related to higher hydration rates. Hence, the use of limestone in cement produces a material that is structurally adequate to be used in construction.     

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.     

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 unburned carbon in palm oil fuel ash on fluidity of cement pastes containing superplasticizer

The aim of this study was to clarify the influence of unburned carbon in palm oil fuel ash (POFA) on the fluidities of cement pastes containing a polycarboxylate-based superplasticizer (SP). The POFA was ground in a ball mill to produce ground POFA (GPOFA). Unburned carbon, which was the major part of unburned residue in GPOFA, was removed by heating at 500 °C for 1 h, producing treated POFA (TPOFA). Neither glassy phase crystallization nor agglomeration of GPOFA particles occurred during the heat treatment. Cement pastes containing GPOFA and TPOFA had lower fluidities than that of ordinary Portland cement (OPC) paste. Cement pastes containing TPOFA had higher fluidities than cement pastes containing GPOFA. Unburned carbon absorbed more SP than did the other particles in the cement pastes because of the carbon’s large specific surface area. Because of their irregular shape and porosity, GPOFA particles absorbed more SP than did OPC particles. Therefore, the higher the content of unburned carbon and GPOFA particles in the cement paste, the greater the quantity of SP needed to be added.     

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.     

Use of natural and thermally activated porphyrite in cement production

The aim of the present study was to investigate the use of porphyrite in the production of Portland cement. Natural and thermally activated porphyrites were used as a clay raw material and an activator, respectively, at 0, 10, 20, 30, 40 and 50 wt% in order to assess their effects on the cement properties. According to the test results, the compressive strength of the specimens decreased with increasing natural porphyrite content in various curing periods. However, the compressive strength of cement produced with 10 wt% porphyrite (activator) activated at 650 °C for 30 min showed a higher value (56 MPa in TPC-6) than cement without activator (51 MPa in RPC-2). Due to thermal activation, porphyrite activator containing a glass phase possesses an enhanced reactivity during clinker hydration that intensifies the synthesis of hydrosilicates and improves compressive strength accordingly. The X-ray diffraction analysis confirmed an intensive formation of Portland cement minerals such as C₃S, β-C₂S, C₃A and C₄AF. The addition of thermally activated porphyrite has also led to an improvement of the rheological behavior, stability to expansion, increase in setting time and decrease in specific surface area of cement. As prepared cement composites and concretes with improved properties meet the requirements of State Standards 310-86 and 10181-81 for Portland cement and concrete, respectively. The findings in this report indicate that porphyrite can be utilized both as a raw material and an activator in the production of cement.     

矿渣粉的粉磨方式对矿渣水泥性能的影响研究

通过激光粒度分析仪（LPS）对球磨和立磨粉磨的矿渣粉粒度分析，旋转粘度计对矿渣水泥流变性能的测量及胶砂强度测定。结果表明：球磨机所加工的矿渣粉比立磨加工的矿渣粉颗粒尺寸分布宽、细颗粒含量高：矿渣粉比表面积相近时，两种矿渣水泥的流变性能相差不大：球磨矿渣水泥的强度比立磨的稍好。     

矿渣粉的粉磨方式对矿渣水泥性能的影响研究

墨西哥绿色建筑协会组织专场演讲会，邀请正在墨西哥参加联合国世界水论坛的中国建设部副部长仇保兴，就中国的建筑节能与绿色建筑的发展发表演讲。仇保兴在演讲中详细介绍了中国绿色建筑发展对世界可持续发展的重大意义、发展目标和基本策略。     

磨细粉煤灰粉磨制度对其水化行为和强度的影响分析

对不同粉磨制度下得到的磨细粉煤灰进行性能表征,并使用磨细粉煤灰制备水泥浆体,进行强度测试和水化产物物相分析。研究结果表明:设有分选系统的立磨制备的磨细粉煤灰粒度更小,而试验室球磨机在粉磨过程中更多球形颗粒被破坏,更易激发出其火山灰活性,增强其在水泥浆体中的水化程度,从而表现出更高的强度。     

Effect of nano-silica on rheology and fresh properties of cement pastes and mortars

Amorphous nano-silica (nS) particles (0–2.5 wt%) by cement were incorporated in cement pastes and mortars, and their effect on the fresh state behaviour was analysed. Rheological tests showed that after 75 min from the mixing start, the mortar having 2.5 wt% nS shows insufficient flowability to allow its continuous monitoring in a Viskomat PC viscometer. The influence of nS content was better observed on yield stress when compared with plastic viscosity values (the first increased about 66.5% while the latter just increased 3.6%). With nS addition, spread, setting time and the moment to reach the maximum temperature decreased 33%, 60% and 51.3%, respectively, when compared with samples without nS. X-ray diffraction showed presence of calcium hydroxide after 9 h in the sample with 2.5 wt% nS. The air content increased 79% and apparent density decreased 2.4% when nS was added.     

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.     

Compressive strength and hydration with age of cement pastes containing dune sand powder

This experimental work has focused on studying the possibility of using dune sand powder (DSP) as a part mass addition to Portland cement. Studying the effect of addition dune sand powder on development of compressive strength and hydration with age of cement pastes as a function of water/binder ratio, was varied, on the one hand, the percentage of the dune sand powder (physico-chemical and chemical effect) and on the other, the fineness of dune sand powder (physical effect). In order to understand better the chemical effect (pozzolanic effect) of dune sand powder in cement pastes, we followed the mixtures hydration (50% pure lime + 50% DSP) by X-ray diffraction. These mixtures pastes present a hydraulic setting which is due to the formation of a C–S–H phase (calcium silicate hydrate). The latter is semi-crystallized. This study is a simplified approach to that of the mixtures (80% ordinary Portland cement + 20% DSP), in which the main reaction is the fixing of the lime coming from the cement hydration in the presence of the dune sand powder (pozzolanic reaction), to form calcium silicate hydrate C–S–H semi-crystallized of second generation. The results proved that up to 20% of dune sand powder as Portland cement replacement could be used with a fineness of 4000 cm²/g without affecting adversely the compressive strength. The dune sand powder, despite its crystalline nature, presents a partial pozzolanic reactivity.     

Preparation and properties of an environment friendly polymer-modified waterproof mortar

A new type of environment friendly polymer-modified waterproof mortar (PMWM) was developed through adding ethylene vinyl acetate (EVA)/vinyl acetate–vinyl ester of versatic acid (Va–VeoVa) mixture (re-dispersible emulsion powder), mine tailings, quartz sand and additives to the eco-cement, which was prepared by grinding the mixture of steel slag, blast-furnace slag, fly ash and activator. The optimal material proportioning of PMWM was obtained based on the Orthogonal experiment: re-dispersible emulsion powder, 11 wt.%; cement–sand ratio, 1:3.5 (tailings/quartz sand = 1:3); EVA/Va–VeoVa ratio, 1:1; water reducing agent (based on the cement weight), 1.5 wt.%. The product conforms to JC/T 984-2005 (China professional standard: Polymer–cement waterproof mortar). Some factors influencing the characteristics of the mortar were discussed.     

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.     

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.     

Influence of activator on the strength and drying shrinkage of alkali-activated slag mortar

The development of new binders, as an alternative to traditional cement, by the alkaline activation of industrial by-products (i.e. ground granulated slag and fly ash) is an ongoing research topic in the scientific community [Puertas F, Amat T, Jimenez AF, Vazquez T. Mechanical and durable behaviour of alkaline cement mortars reinforced with polypropylene fibres. Cem Concr Res 2003;33(12): 2031–6]. The aim of this study was to investigate the feasibility of using and alkaline activated ground Turkish slag to produce a mortar without Portland cement (PC).Following the characterization of the slag, mortar specimens made with alkali-activated slag were prepared. Three different activators were used: liquid sodium silicate (LSS), sodium hydroxide (SH) and sodium carbonate (SC) at different sodium concentrations. Compressive and flexural tensile strength of alkali-activated slag mortar was measured at 7-days, 28-days and 3-months. Drying shrinkage of the mortar was measured up to 6-months. Setting times of the alkali-activated slag paste and PC paste were also measured.Setting times of LSS and SH activated slag pastes were found to be much slower than the setting time of PC paste. However, slag paste activated with SC showed similar setting properties to PC paste.LSS, SH and SC activated slag mortar developed 81, 29, and 36 MPa maximum compressive strengths, and 6.8, 3.8, and 5.3 MPa maximum flexural tensile strengths at 28-days. PC mortar developed 33 MPa compressive strength and 5.2 MPa flexural tensile strength. LSS and SH activated slag mortars were found to be more brittle than SC activated slag and PC mortars.Slag mortar made with LSS had a high drying shrinkage, up to six times that of PC mortar. Similarly, slag mortar made with SH had a shrinkage up to three times that of PC mortar. However, SC activated slag mortar had a lower or comparable shrinkage to PC mortar. Therefore, the use of SC as an activator for slag mortar is recommended, since it results in adequate strength, similar setting times to PC mortar and comparable or lower shrinkage.     

Recycling of the product of thermal inertization of cement–asbestos for the production of concrete

A novel field of research in materials science is the recycling of secondary raw materials for construction and building materials such as concrete. This paper describes the successful recycling of as much as 20 wt% of the product of thermal transformation of cement–asbestos for the formulation of concrete. The main mineralogical phases present in the product of transformation of cement–asbestos are C2S, ferrite, and Al-, Ca-, Mg-rich silicates such as akermanite (ideally Ca₂MgSi₂O₇) and merwinite (ideally Ca₃Mg₂Si₂O₈). The behavior of this secondary raw material, termed KRY·AS, in commercial concrete was investigated using five different mixtures in which various portions (0, 5, 10, 15 and 20 wt%) of cement were substituted by KRY·AS. The results of preliminary technological tests (slump test, compressive strength, flexural strength after 28 days, and depth of penetration of water under pressure after 28 days) were discussed and interpreted with the aid of chemical, mineralogical and SEM analyses.One of the major results is that after 28 days, although all the concrete samples are invariably classified as “ordinary concrete” according to the UNI 6132 tests, those diluted with KRY·AS display a lower resistance to compression with respect to the standard. On the other hand, they recover compressive strength and display values identical to that of the standard after 90 days. The addition of the secondary raw material has the effect to slow down the kinetics of setting/hardening because the main cement phase present in KRY·AS is C2S which has a slower rate of hydration with respect to C3S.     

Cementitious characteristics of hydrated cement paste subjected to various dehydration temperatures

This paper emphasizes on studying the cementitious characteristics and the relative rehydration capability of dehydrated cement paste (DCP). Several specimens of DCP were firstly prepared, respectively after pre-heating the powders of hydrated cement paste (HCP) at different temperatures ranging from 300 °C to 900 °C. The cementitious properties of each DCP were then evaluated by the required water of standard consistency, setting time, degree of rehydration, compressive strength development and microstructure evolution. The experimental results show that DCP has highly required water of standard consistency, short setting time and rapid rehydration rate compared with ordinary Portland cement, and also indicate that the rehydration capacity of DCP is influenced by the dehydration temperature.     

Utilization of bagasse ash as a pozzolanic material in concrete

The physical properties of concrete containing ground bagasse ash (BA) including compressive strength, water permeability, and heat evolution, were investigated. Bagasse ash from a sugar factory was ground using a ball mill until the particles retained on a No. 325 sieve were less than 5wt%. They were then used as a replacement for Type I Portland cement at 10, 20, and 30wt% of binder. The water to binder (W/B) ratio and binder content of the concrete were held constant at 0.50 and 350 kg/m³, respectively.The results showed that, at the age of 28 days, the concrete samples containing 10–30% ground bagasse ash by weight of binder had greater compressive strengths than the control concrete (concrete without ground bagasse ash), while the water permeability was lower than the control concrete. Concrete containing 20% ground bagasse ash had the highest compressive strength at 113% of the control concrete. The water permeability of concrete decreased as the fractional replacement of ground bagasse ash was increased. For the heat evolution, the maximum temperature rise of concrete containing ground bagasse ash was lower than the control concrete. It was also found that the maximum temperature rise of the concrete was reduced 13, 23, and 33% as compared with the control concrete when the cement was replaced by ground bagasse ash at 10, 20, and 30wt% of binder, respectively. The results indicate that ground bagasse ash can be used as a pozzolanic material in concrete with an acceptable strength, lower heat evolution, and reduced water permeability with respect to the control concrete.