Accelerated microstructural evolution of a calcium-silicate-hydrate (C-S-H) phase in pozzolanic pastes using fine siliceous sources: Comparison with historic pozzolanic mortars

Traditional pozzolanic mortars such as those from Rhodes, Greece, or Hagia Sophia, Turkey, revealed the presence of a calcium-silicate-hydrate (C-S-H) binding phase. This phase, which is similar to that found in ordinary Portland cement (OPC), is produced under the pozzolanic reaction of slaked lime with fine reactive siliceous sources at temperatures <100 °C. The traditional siliceous sources were replaced by fumed silica or tetraethyl orthosilicate (TEOS). A microstructural analysis revealed an enhanced reaction rate but similar morphologies of the resultant C-S-H phases, confirming that the reaction-limiting factor is the dissolution of the siliceous sources.     

MSWI ashes as mineral additions in concrete

The paper describes the results of a research aimed at studying the effect of replacing part of portland cement with fly ash and bottom ash, both from municipal solid waste incinerators (MSWIs). Fly ash was subjected to a washing treatment to reduce the chloride content, while bottom ash was subjected to dry or wet grinding underwater. Concretes with addition of different types of ashes, including a traditional coal fly ash (FA), were manufactured. Fresh and hardened properties of the concretes were compared in order to study the advantages and the side effects of each type of addition. Results showed that MSWI bottom ash is potentially attractive as mineral addition for the production of concrete, provided that the risk of entrapment of hydrogen bubbles produced by corrosion of aluminium metallic particles in the fresh concrete is prevented. This could be achieved by wet grinding the bottom ash so that reactions leading to gas development exhaust within the slurry before this is added to the concrete mixture. However, by considering bottom ashes from different incinerators, a great variability was observed in the time required to complete the hydrogen gas production. Nevertheless, when the hydrogen development in the fresh concrete could be avoided, wet ground MSWI bottom showed a good pozzolanic behavior and proved to give a significant contribution to the development of the strength and impermeability of concrete.     

Optimum usage of a natural pozzolan for the maximum compressive strength of concrete

Pozzolans provide an economic production possibility in the concrete industry and improve the properties of concrete, such as durability. Effects of a pozzolan on the properties of concrete vary with the pozzolan type and volume.In this study, effect of a natural pozzolan on the properties of concrete was investigated. Fifteen concrete mixtures were produced in three series with control mixes having 300, 350 and 400 kg cement content. These control mixes were modified to have a combination of 250, 300 and 350 kg cement content and 40, 50, 75 and 100 kg pozzolan addition for 1 m³ concrete. The efficiency of the pozzolan was obtained by using Bolomey and Feret strength equations on 28-day-old concretes. Maximum pozzolan amount with the optimum efficiency was determined. This study shows that the efficiencies obtained from each strength equations are similar and these values decrease with the increase of pozzolan/cement ratio.     

Effect of ternary binder on the mechanical and microstructural properties of sand concrete

The present work focuses on the study of effect of the cement content (C), lime (L) and pozzolan (P) as well as the effect of their combinations C*L, C*P and L*P on the mechanical and microstructural properties of sand concrete based on a ternary binder using the ‘mixture design’ method. C, L and P were taken as independent variables, while the flexural strengths (Rf) and the compressive strengths (Rc) at 7 and 28 days were taken as responses. Mathematical models were determined. The obtained results showed that the most significant variable that affects all the studied responses is the cement content. The SC09 (100% C) presented the highest values. However, the SC08 (80% C + 20% L) ranks second and the SC13 (80% C + 20% P) ranks third in terms of mechanical strength. But SC08 and SC13 provided 20% of cement economy, while the minimum values of mechanical strength were recorded in the case of SC17 (100% L), which means that a high rate of lime has relatively a negative influence on the mechanical strength. On the other hand, the X-ray diffraction study showed that the type of the resulting hydration products and their quantities depend on the proportions of C, L and P, which justifies the changes recorded in the properties studied. Finally, the microscope visualization showed also that the material appears relatively homogeneous and dense with a good adhesion paste-aggregate, either in the case of cement or pozzolan or lime.     

Effect of material characteristics on the properties of blended cements containing high volumes of natural pozzolans

The effect of three different natural pozzolans from Turkish deposits on the properties of blended cements produced by intergrinding cement clinker with a high volume of natural pozzolan (55 wt.% of the cementitious material) was investigated. The particle size distribution of blended cements, setting time, heat of hydration, and compressive strength of blended cement mortars were determined. Experimental results showed that the hardness of the pozzolanic material strongly influenced the particle size distribution and the related properties of the blended cements by affecting the fineness of the components of the blended product. The early strength of the mortars was strongly affected by the particle size distribution of blended cements, whereas the strength development performance of the mortars was more related to the pozzolanic activity of the natural pozzolan present in the blended cement.     

Physical performances of blended cements containing calcium aluminosilicate glass powder and limestone

This work explores the suitability of calcium aluminosilicate (CAS) glass particles as an alternative to conventional supplementary cementitious materials (SCMs) such as fly ash and blast furnace slag. The reason for adding CAS glass particles to the cement blend is to reduce the CO₂ emission of cement production at the same level of performance. For this purpose, blended cement mortars containing 30 wt.% clinker replacement are characterized with respect to workability and mechanical performance. The results indicated that real emission reductions are possible, particularly for combinations of finely ground limestone and CAS glasses which resulted in significantly higher strengths than would be predicted from the individual contributions of each constituent.     

Enhancement of lime reactivity by addition of diatomite

Diatomite was used as a Pozzolan to augment lime reactivity. This was confirmed through laboratory wet and dry flue gas desulfurization (FGD) experiments using pH-stat apparatus (representing wet FGD) and fixed bed reactors (representing dry FGD). BET surface area analysis and SEM imaging were used in characterization and to aid in understanding the behavior of the sorbent. After affirming that diatomite improves lime's reactivity, optimization tests were conducted to maximize the reactivity output. The effect of various variables namely; temperature, lime to diatomite ratio, solid to liquid ratio and stirring speed, were maximized linearly, quadratically and interactively. The design of optimization experiments was done through design expert software. Central cubic design was used for regression analysis. As expected, temperature had the highest effect towards reactivity. Some effect showed a mini-max behavior while others had a sinusoidal trend.     

Opal-A rich additives used in ancient lime mortars

Ancient stone and brick masonry mortars from three monuments in Konya, Central Anatolia dated to the Anatolian Selçuk Period (12th and 13th centuries AD) were examined for their raw material composition and durability characteristics to understand some characteristics of medieval mortar technology.Optical microscopy, XRD, SEM, EDX, FTIR and TGA analyses revealed that the mortars contained high percentage of lime binder totally carbonated into micritic calcite. Coarse and medium aggregates were mainly composed of sandstone and metamorphic rock fragments, quartz, feldspar and mica minerals. Opal-A was found in considerable amounts in the fine aggregates, likely not derived from the coarser ones but added separately. Pozzolanic activity of the fine aggregates was determined by conductometric measurements. Their ability to form C-S-H was observed by treating them with saturated Ca(OH)₂ solution.Bulk density and total porosity measurements showed that the mortars were highly porous due to the use of high amount of lime. On the other hand, they possessed sufficient mechanical strength. Mechanical properties were determined by point load tests and ultrasonic pulse velocity measurements. They were expressed as uniaxial compressive strength (UCS) and modulus of elasticity (E_mod) in MPa.The results were also discussed in terms of durability characteristics of the mortars. They were expressed with the use of uniaxial compressive strengths in dry and wet states, and total porosity values. The mortars were considered to have high durability to wetting and drying cycles but had poor durability to the crystallization of water-soluble salts.     

Recycling of silicomanganese slag as pozzolanic material in Portland cements: Basic and engineering properties

Correct use of SiMn slags requires a detailed knowledge of their properties, as chemical and mineralogical composition, pozzolanic activity, reaction kinetics, setting time, volume expansion and strength play important role in the final valorisation of SiMn slag as pozzolanic material. This kind of slag is formed mainly of SiO2 and CaO, followed by Al2O3 and MnO which sum is nearly 90%. Sulphites content of 0.42% was detected. The main crystalline compound identified in SiMn slag is akermanite.The results obtained show that SiMn slag blended cements do not show volume instability, the strength values are very close to the control mortar and they have a denser matrix. SiMn blended matrices fulfil standard specification requirements (chemical, physical and mechanical ones) and show that SiMn slag is suitable for blended cements manufacture.     

Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan

Pozzolanic activity of clinoptilolite, the most common natural zeolite mineral, was studied in comparison to silica fume, fly ash and a non-zeolitic natural pozzolan. Chemical, mineralogical and physical characterizations of the materials were considered in comparative evaluations. Pozzolanic activity of the natural zeolite was evaluated with various test methods including electrical conductivity of lime-pozzolan suspensions; and free lime content, compressive strength and pore size distribution of hardened lime-pozzolan pastes. The results showed that the clinoptilolite possessed a high lime-pozzolan reactivity that was comparable to silica fume and was higher than fly ash and a non-zeolitic natural pozzolan. The high reactivity of the clinoptilolite is attributable to its specific surface area and reactive SiO₂ content. Relatively poor strength contribution of clinoptilolite in spite of high pozzolanic activity can be attributable to larger pore size distribution of the hardened zeolite-lime product compared to the lime-fly ash system.