Durability performance potential and strength of blended Portland limestone cement concrete

This paper describes a study on the durability potential and strength of composite Portland-limestone cement (PLC) concrete mixtures blended with ground granulated blast furnace slag (GGBS) and/or fly ash (FA). Their performance was compared against ordinary Portland cement, plain PLC and Portland-slag cement concrete mixtures. Using the South African Durability Index approach, results indicate reductions in the penetrability of the composite PLC blends compared to the other mixtures. The durability indicators are chloride conductivity, gas (oxygen) permeability and water sorptivity. Compressive strength of the composite PLC mixtures containing both GGBS and FA showed competitive performance with the comparative mixtures, but FA blended PLC mixtures had diminished compressive strength values. The paper also presents considerations on the practical implications of using blended PLC concrete mixtures.     

Properties of binary and ternary blended cement mortars containing palm oil fuel ash and metakaolin

Abstract

This paper has investigated the properties of mortars made from binary and ternary blends of metakaolin (MK), palm oil fuel ash (POFA), and ordinary Portland cement (OPC). A total of 17 different mortar mixtures were produced. The OPC in the mixtures was partially replaced by MK, POFA, or a combination of MK and POFA at different replacement levels of (0–30%) by weight of the binder. At the fresh state, the flow (workability) of mortar mixtures was determined, while at the hardened state, the compressive strength and porosity at the ages of 7, 28, and 90 days were evaluated. The results showed that the flow of mortar is boosted with the combined use of MK and POFA compared to when MK is separately used. Besides, improvement in low early compressive strength development and reduction in high porosity from use of POFA occurred with the addition of up to 10% MK content. Therefore, the combination of POFA and MK could be used as a supplementary cementitious material to produce cement-based material of higher quality than OPC.     

Sulfate resistance of plain and blended cement

This paper presents a laboratory study on the sulfate resistance of blended cement combination of reference Portland cement with high volume ground granulated blast-furnace slag (GGBS) and natural pozzolan (NP). The exposure solutions were tap water containing 5% magnesium sulfate solution and 5% sodium sulfate solution. Two types of grinding method (separately grinding and intergrinding, two finenesses (250 m²/kg and 500 m²/kg) and three different proportions (10%, 20%, and 30% by weight of mixture)) of each of two different additives (GGBS and NP) in equal amounts were employed. In addition to these blends, plain Portland cements without additives were prepared as references specimens. Standard Rilem sample size (40 mm × 40 mm × 160 mm) was used for the experimental study.It was observed that the sulfate resistances of blended cements were significantly higher both against sodium sulfate and magnesium sulfate attacks than references cement. Final strength reductions for finer mixes attacked by magnesium sulfate were marginally lower than those attacked by sodium sulfate. On the other hand, no particular relation was found between the sulfate resistance of the mortars and the grinding methods.     

Susceptibility of Portland cement and blended cement concretes to plastic shrinkage cracking

The market share of different types of blended cements is increasing year by year. Generally, blended cements are ground to higher fineness and exhibit a slower development of mechanical properties compared to Ordinary Portland Cement (OPC), which might affect the concrete performance in terms of shrinkage cracking at early ages.In this paper, the performance of concretes made with different cement types is compared according to the ASTM C1579-13 standard for plastic shrinkage cracking. The cracking behavior was further correlated to the deformations of both unrestrained and restrained specimens measured by a 3D image correlation system. The main factors influencing the cracking behavior were discussed based on poromechanics. It is concluded that the bulk modulus evolution has a dominant effect on controlling the plastic shrinkage cracking. Concretes made of more reactive cements, in particular with higher clinker content, are less susceptible to plastic shrinkage cracking. For cements with the same clinker content, increasing the cement fineness reduces the risk of plastic shrinkage cracking.     

Properties of self-compacting portland pozzolana and limestone blended cement concretes containing different replacement levels of slag

In order to reduce energy consumption and CO₂ emission, and increase production, cement manufacturers are blending or inter-grinding mineral additives such as slag, natural pozzolana, and limestone. This paper reports on the results of an experimental study on the production of self-compacting concrete (SCC) produced with portland cement (PC), portland pozzolana (PPC) and portland limestone (PLC) blended cements. Moreover, the effect of different replacement levels (0–45%) of ground granulated blast furnace slag (GGBFS) with the PPC, PLC, and PC cements on fresh properties (such as slump flow diameter, T ₅₀₀ slump flow time, V-funnel flow time, L-box height ratio, setting time, and viscosity) and hardened properties (such as compressive strength and ultrasonic pulse velocity) of self-compacting concretes are investigated. From the test results, it was found that it was possible to manufacture self-compacting concretes with PPC or PLC cements with comparable or superior performance to that of PC cement. Furthermore, the use of GGBFS in plain and especially blended cement self-compacting concrete production considerably enhanced the fresh characteristics of SCCs.     

Simulation of silica fume blended cement hydration

A model is proposed in this paper to simulate silica fume (SF) blended cement hydration based on the kinetics, stoichiometry and physical chemistry of cement hydration and pozzolanic reaction. The pozzolanic reaction degree, volume fraction of hydration products, capillary porosity and gel porosity can be obtained from model simulation. By using proper amount of silica fume replacement, the microstructure of silica fume blended cement paste is improved since the volume fraction of C-S-H gel is increased, Ca(OH)₂ content and capillary porosity are decreased due to pozzolanic reaction compared with ordinary Portland cement (OPC) paste. The effects of silica fume particle size, glass phase content and the percentage of silica fume replacement on pozzolanic reaction degree, volume fraction of hydration products, and capillary porosity are simulated. The simulation results show that finer silica fume particles with higher glass phase content (GP) are of higher reactivity. There is an optimum silica fume replacement; extra silica fume only acts as inert filler because there is no enough Ca(OH)₂ from cement hydration to react with it pozzolanically.

---

Résumé Le modèle proposé dans cet article simule l'hydratation de ciment mélangé à de la fumée de silice et est basé sur la cinétique, la stoichiométrie et la physico-chimie de l'hydratation du ciment et la réaction pozzolanique. Le degré de réaction pozzolanique, la fraction volumique des produits de l'hydratation, la porosité capillaire et la porosité de gel peuvent être obtenues par un modèle de simulation. En utilisant la bonne quantité de remplacement de fumée de silice, la microstructure de la fumée de silice mélangée à la pate de ciment est améliorée étant donné que la fraction volumique du gel C-S-H augmente, que le taux de Ca(OH)₂ et la porosité capillaire décroissent en raison de la réaction pozzolanique lorsque l'on compare avec une pate de ciment à base de Portland ordinaire (OPC). Les effets de la taille des particules de fumée de silice, le contenu de la phase de verre et le pourcentage de remplacement de fumée de silice sur le degré de réaction pozzolanique, la fraction volumique des produits d'hydratation et la porosité capillaire sont simulés. Les résultats de cette simulation montrent que de plus fines particules de fumée de silice avec une plus grande quantité de phase de verre (GP) sont de forte réactivité. Il existe un remplacement de fumée de silice optimal; de la fumée de silice en plus ne sert que de filler inerte car il n'y a pas assez de Ca(OH)₂ à partir de l'hydratation du ciment pour provoquer une réaction pozzolanique

     

Hydration and properties of nano-TiO2 blended cement composites

Two types of nano-TiO₂ particles were blended into cement pastes and mortars. Their effects on the hydration and properties of the hydrated cement pastes were investigated. The addition of nano-TiO₂ powders significantly accelerated the hydration rate and promoted the hydration degree of the cementitious materials at early ages. It was demonstrated that TiO₂ was inert and stable during the cement hydration process. The total porosity of the cement pastes decreased and the pore size distribution were also altered. The acceleration of hydration rate and the change of microstructure also affected the physical and mechanical properties of the cement-based materials. The initial and final setting time was shortened and more water was required to maintain a standard consistence due to the addition of the nano-TiO₂. The compressive strength of the mortar was enhanced, practically at early ages. It is concluded that the nano-TiO₂ acted as a catalyst in the cement hydration reactions.     

Accelerated strength and testing of concrete using blended cement

Accelerated strength testing using the boiling water procedure of ASTM C 684 was performed to evaluate this test method for use in the routine quality control of concrete made of local materials with particular emphasis on the use of blended cements, and in the prediction of potential quality and strength of concrete at later ages. Large number of groups of standard concrete specimens are sampled; in each group one cube represented the accelerated strength and is tested at 28.5 h while the other one is normally cured and tested at 28 days. Test results were recorded and statistically evaluated. A computer program was developed to carry out the numerical statistical computations and regression analysis. Correlation between the 28-day compressive strength and the corresponding accelerated strength was established considering the utilization of local materials and practices. The outcome of this study in the form of prediction models confirm that accelerated strength testing could be accepted in lieu of the standard 28-day testing. The conclusions derived may provide experimental evidence in favor of implementing the standard boiling water method for use in relation to quality control and prediction of concrete strength at later ages. Advanced Cement Based Materials 1997, 5, 49–56.     

Flash-calcined dredging sediment blended cements: effect on cement hydration and properties

Dredging of docks and waterways generates a large and continuous supply of sediments currently destined for disposal. Transforming this currently wasted materials into new resources still requires meeting technical challenges. One of the options is to process the sediments into a supplementary cementitious material by flash-calcination. This paper describes the effect of cement replacement by flash-calcined dredged sediments on cement hydration and key properties. The hydration kinetics, products and microstructure are studied to explain changes in cement properties such as compressive strength development and workability. The flash-calcined dredging sediments show clear pozzolanic activity which surpasses that of typical coal combustion siliceous fly ash (V, EN 197-1). This is manifested in (1) the rate of compressive strength development, (2) reduced portlandite and (3) increased ettringite and bound water contents. The results show that calcination can transform wasted dredging sediments into a new supplementary cementitious resource for producing large volumes of low-CO₂ blended cements.     

Effect of grinding of low-carbon rice husk ash on the microstructure and performance properties of blended cement concrete

The effectiveness of unground low-carbon rice husk ash (URHA) as a pozzolan and the effect of grinding the URHA to finer fractions for use in portland cement system were investigated. The properties investigated include the setting time and calcium hydroxide depletion of rice husk ash (RHA) pastes; microstructure and flow behavior of RHA mortars; strength and durability of RHA concretes. Results from this investigation suggested that the URHA and ground RHA (GRHA) mixtures performed better than the control mixtures in all tests conducted except water demand and setting time. The URHA mixture revealed denser microstructure compared to the control mixture. The internal porosity created by the coarse RHA grains in the matrix and their inability to completely participate in pozzolanic reaction may be the reasons for the poorer performance of the URHA mixture than compared to the GRHA mixture. The effect of grinding the RHA to finer fractions either substantially or slightly improved all properties except final setting time. With the performance of the GRHA concrete somewhat similar to that of the SF concrete, the use of ground RHA can be concluded to provide acceptable performance in portland cement systems.     

Properties of Metakaolin blended cements

Metakaolin is a supplementary cementitious material with pozzolanic properties. Its activation by triacalcium silicate (C₃S), triacalcium aluminate (C₃A), and ordinary Portland cement is reported. The early hydration period of pastes containing metakaolin was investigated using isothermal calorimetry and conductivity. Differential thermal analysis, X-ray diffraction, and Fourier transform infrared spectrometry were used to follow the consumption of calcium hydroxide (CH) and identify the products of reaction. Compressive strength and porosity were also determined. The results show that CH is quickly consumed, the microstructure is rich in CSH and strätlingite (C₂ASH₈), and the pore size distribution is displaced toward smaller values. Advanced Cement Based Materials 1994, 1, 161–168     

硅烷偶联剂改性MDF水泥的水敏性研究

为了改善MDF水泥的水敏性，以N-β-(氨乙基)-γ-氨丙基三甲氧基硅烷偶联剂对高铝水泥-聚乙烯醇基MDF水泥进行化学改性，测试了硅烷偶联剂改性MDF水泥的力学性能及耐水性，分析了改性MDF水泥的孔结构，并与未改性同种MDF水泥进行比较．结果表明：MDF水泥经硅烷偶联剂改性后，不仅抗弯、抗压强度、断裂韧性和微区硬度提高，孔隙减少，结构致密，而且表现出良好的耐水性，水浸泡90d的抗弯强度保持率由改性前的38%提高到改性后的80%，同时吸湿量和水的扩散系数下降。     

The hydration of slag,part 2: reaction models for blended cement

The hydration of slag-blended cement is studied by considering the interaction between the hydrations of slag and Portland cement clinker. Three reaction models for the slag-blended cement are developed based on stoichiometric calculations. These models correlate the compositions of the unhydrated slag-blended cement with the quantities and compositions of the hydration products. The model predictions are further used to calculate some properties of hydrating slag cement pastes, including the molar fractions of products, the water retention, chemical shrinkage and porosities of pastes. The models are validated by comparing the model predictions with the measurements and proven to be successful in quantifying the hydration products, predicting the composition of the main hydration product (C-S-H) and calculating the properties of the hydration process. The model predictions show that as the slag proportions in the blended cement changes, water retention in the hydration products changes only slightly if compared to that of Portland cement, but the chemical shrinkage can vary in a wide range, depending on the slag hydration degree in the cement.     

Carbonation durability of blended cement pastes used for waste encapsulation

Blended cement pastes are currently used for encapsulation of low level and intermediate level nuclear waste in the UK. However, there is still little information on the long-term durability of those mixes to some chemical attacks. Accelerated testing may predict the long-term durability or at least help the selection of more durable formulations. In this work, blended blastfurnace slag (BFS)/Portland cement (OPC) pastes containing 60, 75 and 90% BFS and pulverised fuel ash (PFA)/OPC pastes with 40, 55 and 75% PFA were cured at 20 and 60°C for 90 days then submitted to natural and accelerated carbonation (5% CO₂). The effects of the curing temperature as well as the OPC replacement level on the carbonation ratio are presented. Results showed a good correlation between natural and accelerated carbonation for the pastes studied. Carbonation was found to be governed by the amount of calcium hydroxide available in the mixes before the process started.     

Efficient utilization of cementitious materials to produce sustainable blended cement

To achieve sustainable development of cement industry, cementitious efficiency of different cement clinker and supplementary cementitious materials (SCMs) fractions, in terms of hydration process and strength contribution ratio, was characterized. The results show that blast furnace slag and steel slag should preferably be arranged in fine fractions due to their desirable hydration processes and high strength contribution ratios. Cement clinker should be positioned in intermediate fraction (8–24 μm) due to its proper hydration process. Replacement of cement clinker by SCMs with low activity or inert fillers in coarse fractions was also suggested, because coarse cement clinker fractions gave very low hydration degrees and little strength contribution. Both early and late properties of gap-graded blended cements prepared can be comparable with or higher than those of Portland cement, indicating both cement clinker and SCMs were used more efficiently. These blended cements also give additional cost savings and reduced environmental impact.     

Strength development of ternary blended cement with limestone filler and blast-furnace slag

The benefits of limestone filler (LF) and granulated blast-furnace slag (BFS) as partial replacement of portland cement are well established. However, both supplementary materials have certain shortfalls. LF addition to portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. On the other hand, BFS contributes to hydration after seven days improving the strength at medium and later ages.Mortar prisms in which portland cement was replaced by up to 20% LF and 35% BFS were tested at 1, 3, 7, 28 and 90 days. Results show that the contribution of LF to hydration degree of portland cement at 1 and 3 days increases the early strength of blended cements containing about 5–15% LF and 0–20% BFS. The later hydration of BFS is very effective in producing ternary blended cements with similar or higher compressive strength than portland cement at 28 and 90 days. Additionally, a statistical analysis is presented for the optimal strength estimation considering different proportions of LF and BFS at a given age. The use of ternary blended cements (PC–LF–BFS) provides economic and environmental advantages by reducing portland cement production and CO₂ emission, whilst also improving the early and the later compressive strength.