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In this exploratory study, the effects of nano silica (NS) on the properties of self-compacting pastes (SCPs) incorporated with superabsorbent polymer (SAP) have been investigated. NS was added to cement pastes, containing SAP, in varying amounts of 1%, 2% and 3%. SAP were found out to be successful in mitigating shrinkage in all formulations; however they were more effective in mixes without super-plasticizers (SPs). SAP particles reduced the fluidity, increased the air content and also reduced strength slightly due to the formation of macro-pores. NS was beneficial in improving the hydration attributes by increasing the mechanical strength and refining the microstructure. The denser microstructure of the NS modified pastes compensated for the macro pore formation associated with SAP incorporation, leading to strength increase. With NS, there was better bonding of the SAP particles in the matrix. The reduced Ca(OH)2 content in NS modified samples showed increased pozzolanic activity associated with NS in cement pastes.

The present study investigates the influence of limestone powder, fly ash, zeolite powder, and their blends on some fresh and hardened properties of self-compacting (SC) mortars. Blends of supplementary cementitious materials (SCMs) perform better than a single SCM in cementitious systems. The motivations for the present study include the introduction of novel blends of SCMs like limestone and zeolite powders to provide efficient SC mortars and potential alternatives of fly ash in a period of its short supply. The investigated properties include flow characteristics, shrinkage, pore pressure, hydration kinetics, compressive strength, microstructural characteristics using MIP and SEM, compositional analysis using thermo-gravimetric analysis, hardened density, and relative water absorption. The experimental results indicate that 20% replacement of cement with blend of limestone and zeolite powders led to the most improved response and provided better performance than other studied compositions.

This experimental study explores the feasibility of the development of eco-friendly self-compacting cementitious systems, utilizing wood waste sawdust (SD), for sustainable building construction. Two different gradations of SD viz-a-viz, coarse SD (CSD) and fine SD (FSD) were used in modifying neat Portland cement paste system as partial replacement of cement, in various weight fractions of 2%, 5%, and 7%. The fresh and hardened state properties of SD modified paste were determined. The results indicated that despite the strength reduction with SD addition in cement paste (strength decrease of 11%–34% was observed with SD addition), the resulting shrinkage strain is greatly reduced owing to the higher water absorption of SD particles thus increasing the water demand, to maintain self-compactibility, as well. The reduction in shrinkage of SD modified pastes was significant, with a reduction range of 45%–80%, as compared to control sample. Density and unit weight of the developed pastes were also reduced. The ability of SD to absorb water and releasing it later, thus providing moisture for cement hydration, suggests that SD has the potential to serve as an internal curing agent in self-compacting cementitious systems. Utilizing SD in cementitious binders may, then, not only promote sustainable development, but also lead to more durable infrastructures.

This paper shows the response of self-compacting paste systems (SCPs) containing botanical Acacia Modesta (AM) gum, a natural organic ooze-out of an indigenous tree called Phulai, as an admixture. The gum being different in its nature and origin, exhibited different results from Acacia Nilotica gum powder when used in SCPs. AM gum powder was characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). The self-compacting paste systems (SCPs) containing 0.25%, 0.5%, 0.75% and 1% AM gum powder were tested for super-plasticizer (SP) demand, flow, viscosity, air content (in fresh state), density, total linear early shrinkage, calorimetry and both short-term (28-day) and long-term (90-day) compressive strengths. SCPs with AM gum powder showed a considerable decrease in total shrinkage, a reduction in density values, an increase in fresh state viscosity. AM gum powder also had a retarding effect on setting times of the respective gum modified SCPs. Moreover, the electrical resistivity of samples containing AM increased tremendously indicating change in the microstructure of the gum modified SCP systems. It became clear that different types of Acacia gums when incorporated in SCPs gave different responses and should be used with complete understanding. Therefore, AM gum in cementitious systems offers many potential areas for application and further future research work. The AM gum powder may be used for reducing shrinkage in SCP systems, establishing internal curing inside the SCCS, for enhancing the viscosity of the cementitious systems and for producing slightly porous energy efficient cementitious systems.

Cement is a source of anthropogenic emissions ensuing environmental concerns and susceptible to crack under stresses. For mitigating the durability concerns, a bio-influenced effective microorganisms technology (EMs) has been employed in the cementitious composites. In the present research, the effect of EMs on the properties of self-compacting and conventional cementitious composites was explored using three types of EMs (EM1®, EMC® and EMX-Ceramics®) with three different of cements (CEMI, CEMIII and Calcium Aluminate cement). Taguchi approach of experimental design was implemented for optimization of formulations. L18 (21 × 37) orthogonal array was selected based on influencing factors namely w/c ratio, cement type, EMs type and EMs percentage replacement. Specimens were casted and cured in air, moisture and desiccator. Forensic inspections were performed to monitor the growth of hydration products and precipitation of bio-calcite precipitate. Energy performance of EMs modified composites was also analyzed using ECOTECT. Experimental results were analyzed statistically using analysis of variance (ANOVA). The analysis revealed that w/c and EM % replacements as the most governing parameters in response modification of cement composites. The 4% EM replacement was determined to be the optimal percentage in refining the fresh and hardened state response of cementitious systems. Forensics endorsed the microstructural refinements as a result of bio-precipitate, contributing in the increase of mechanical properties and reduction in 27% cooling loads. Moreover, theoretical equations were proposed for prediction and optimization of mix design based on Taguchi approach using extensive regressions.

Effective Microorganism technology (EMT) is of Japanese origin and has found useful applications in agriculture and water treatment works. This study reports the response of self-compacting paste systems with the addition of a mixture containing three micro-organisms namely lactic acid bacteria, photosynthetic bacteria and yeast all present in a suitable liquid medium. Two types of Effective Microorganisms (EMs) consortia, EM-Light (EML) having light brown color and low microbial cell concentration and EM-Dark (EMD) having dark brown color with high microbial cell concentration in a suitable liquid were used to study a total of seven self-compacting paste (SCP) formulations. These seven formulations include a control formulation and six EM modified SCP formulations containing 5, 10 and 15% (by wright content of cement) of both EM liquid consortia. The results showed that both EM consortia modified the plastic viscosity, delayed setting times and hydration kinetics, modified volume stability, reduced water absorption of SCP systems in hardened state and enhanced the compressive strength of SCP systems. Especially strength of SCPs with EMD seem to depend on fresh density of the paste to a large extent while with EML it shows different response. An increase of 26% in strength was observed compared to the control formulation with 15% EMD amendment at similar water-cement ratio along with a reduction in water absorption of hardened SCPs which may be attributed to the refinement in microstructure obtained by the production of calcium carbonate predominantly as a result of the reaction between microorganisms and calcium hydroxide. Scanning electron microscopy (SEM) and XRD results also suggest improvements in strengths of SCPs due to calcite (calcium carbonate).

This research characterizes the gum obtained as a natural organic ooze-out from Acacia Nilotica trees, indigenously known as “Keekar”, through Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR) experimental techniques. It reports the response of self-consolidating paste systems (SCPs) containing Acacia Nilotica Gum (AG) in powdered form in ratios of 0.33%, 0.66% and 1% by weight of cement. The results are of interest to construction and civil engineering professionals and showed that AG enhanced the viscosity of SCPs which in turn improves their stability. Also, AG addition increased the water demand, setting times and early age expansion of SCPs while the heat of hydration, density and compressive strength got reduced. Reduction in density is attributed to incorporation of air voids and this may be exploited in energy efficient infills of buildings and possible improved freeze-thaw resistance. Most of the lost compressive strength due to AG incorporation was regained with the addition of Secondary Raw Materials (SRMs) including fly ash (FA) and limestone powder (LSP).

Good workability at construction site is most important aspect of self-compacting concrete. But long delivery times can cause slump loss, which is more pronounced when mineral additives are incorporated into the concrete system. The aim of this paper is to study the effects of prolonged mixing on the flowability and slump retention under action of a high-performance polycarboxylic (PEC)-based superplasticizer used in self-compacting paste systems (SCPs) incorporating various secondary raw materials (SRMs). Experimentation for this research paper was focused on mixing times and slump retention of SCPs incorporating ASTM Class F fly ash (FA), silica fume (SF) and locally available marble powder (MP). While experimenting with SCPs, total mixing time was first restricted to 3 min of mixing to achieve the target flow of 30±1 cm, which was then prolonged to total mixing time of 10 and 20 min keeping the superplasticizer content constant, which showed a more enhanced flow with reduced timing due to better activation of superplasticizer, or enhanced workability but showed some traces of bleeding in the formulations containing MP. The samples were thereafter prepared for strength measurement as per EN-196. Parameters like flow response, strength and microstructures were studied by varying two basic factors in progression: shear time and hold time. Hydration kinetics were also affected by prolonged mixing, and it also decreased the initial and final setting time. FA showed better rheological behaviour upon extended mixing regimes as compared to SF or any other SRMs.

Volatile species (e.g. Na-,K-,Cl-, and S) are released during thermal conversion of coal causing eventual problems such as fouling, slagging and corrosion, especially in gas turbines, on super heaters and in the colder part of heat recovery systems. Thermodynamic study of the released inorganic compounds is supportive before eventually launching experimental work. Therefore, thermodynamic equilibrium was calculated using FactSage 5.2, simulating combustion conditions at elevated pressure (5, 10 and 15 bar) and elevated temperature (1000, 1400 and 1600°C). Their releasing order of various volatile species was estimated by plotting mole fraction of each species at temperature 1000°C and pressure 1 bar. These calculations predict that SO2 is the most stable species for combustion. At all pressure the lowest amount of NaCl and KCl volatilized for LKH and THR lignite char. Evolution of NaCl, KCl and HCl depends on the amount of Cl present in both lignite chars. Key words: Combustion, fact sage, equilibrium calculations, release of volatile species.

Cement and concrete composites are inherently brittle and exhibit very less tensile/flexural strength capacity as compared to their compressive strength. Use of thoroughly dispersed carbon nanotubes in the concrete matrix is one of the possible solution for enhancing mechanical properties in tension/flexure. In the present research work, small fractions of multiwall carbon nanotube (MWCNTs) i.e. 0.05 and 0.10 wt% of cement have been integrated into the cement concrete to study their effect on the mechanical properties of the resultant concrete mixtures. The enhanced performance of the whole mix lies on a single point that MWCNTs must be thoroughly disperse in the mixture. Hence, special arrangement through usage of high energy sonication along with amended acrylic based polymer (performing as a surfactant) was made to have a uniform dispersion of MWCNTs in the concrete mix. The testing of concrete samples includes i.e., flexure, splitting tensile and compressive strengths after 3, 7, 28 and 56 days of curing. After having comparison with the control mix cured for 28 days, it was observed that the addition of 0.05 wt% MWCNTs increased the splitting tensile strength by 20.58%, flexural strength by 26.29% and compressive strength by 15.60%. Through above results, which verify the increase in concrete mix strength after adding MWCNTs, these MWCNTs may be incorporated in the treatment of Nano/micro cracks completed through process of connecting, branching and pinning. Similarly, as proved in three-point bending tests, MWCNTs also enhances the breaking strains as well as the fracture energy of the concrete mixes, besides, imparting increase to the strength. The investigations have shown that incorporating lesser amounts of MWCNTs i.e., 0.05 and 0.10 wt% of cement to the concrete mixes after insuring there complete dispersion, unusually improve their properties like mechanical strengths and fracture behavior.

This paper assesses the mechanical and structural behavior of self-consolidating lightweight concrete (SCLWC) incorporating bloated shale aggregate (BSA). BSA was manufactured by expanding shale pellets of varying sizes by heating them up to a temperature of 1200 &deg, C using natural gas as fuel in the rotary kiln. Fly ash (FA) and limestone powder (LSP) were used as supplementary cementing materials (10% replacement of cement, each for LSP and FA) for improved properties of the resulting concrete. The main parameters studied in this experimental study were compressive strength, elastic modulus, and microstructure. The fresh-state properties (Slump flow, V-funnel, J-Ring, and L-box) showed adequate rheological behavior of SCLWC in comparison with self-consolidating normal weight concrete (SCNWC). There was meager (2&ndash, 4%) compressive strength reduction of SCLWC. Lightweight aggregate tended to shift concrete behavior from ductile to brittle, causing reduced strain capacity and flexural toughness. FA and LSP addition significantly improved the strength and microstructure at all ages. The study is encouraging for the structural use of lightweight concrete, which could reduce the overall construction cost.

A study is reported on a two lane in-service pre-stressed concrete bridge having susceptible vibrations under service traffic conditions. The bridge was 1300 ft long with thirteen simple pre- cast post tensioned spans resting on in-situ bridge piers. The client reported significant vibrations under service loads and requested a solution. The bridge did not have a top wearing surface. Bridge design drawings were provided. The methodology of health assessment included the visual inspection followed by analysis with the help of drawings provided by the client. The records of concrete strengths along with prestressing protocols were missing. The static and dynamic bridge response using static and moving three different loaded vehicles (over loaded tractor trolley, unloaded 5 Axle vehicle loaded trailer and loaded 5 axle trailers) was monitored. Core samples from the bridge deck were taken. NDT, Digital half-cell and electrical resistivity readings were taken at various locations of bridge. The results indicated some design inadequacies, faulty construction methodologies, improper maintenance and lack of awareness even by the professionals to deal with such structures. The remedial measures were suggested in terms of strengthening and maintenance of bridge.

Because concrete and mortars both contain aggregate phase, it may be expected that the trend of results obtained from mortar formulations should be similar to those of concrete or vice versa. Many researchers have used either limestone powder (LSP) or fly-ash (FA) in self-compacting concrete systems. However the present study shows that using either of these secondary raw materials (SRMs) in self-compacting mortar systems does not produce an optimized response. However mixing LSP and FA in suitable proportions and then using this blended SRM enhances the response of self-compacting mortar systems as both FA and LSP seem to complement the properties of each other especially the negative ones. The formulations contain two base SRMs (limestone powder and fly-ash) and in others these two basic SRMs have been replaced at 20% of their mass by some other SRMs or their combinations. Parameters like flow, strength, microstructure, relative water absorption and early volume stability of self-compacting mortar systems have been studied. The results indicate that self-compacting mortars using blended secondary raw material of limestone powder and fly-ash had an improved overall response than those using either of them.

A number of papers on various aspects of SCC can be found in the literature but most of them are based on the laboratory investigations using optimized conditions, complex terminologies and procedures. The results so obtained are not easy to comprehend and are unsuitable for engineers hying to make use of this wonderful technology of the decade. A laboratory SCC mix generally gives a different response when used at a ready-mixed concrete plant. This is due mainly to the differences in mixing regimes, procedures, climatic conditions and aggregate surface moisture estimation. The information provided in this paper is based on the experience gained from laboratory and plant mixes with subsequent field placements 150 meters below the ground level, in a local tunnel of a research and teaching mine, by means of pumping. The total horizontal pumping distance (above and below ground level) was also 150 meters. 50 liter laboratory mixes of combination type of SCC using natural aggregates with different gradings, cement types as well as mineral and chemical admixtures were made and tested followed by the tests on 1.5 or 3.0 m 3 ready-mix plant batches with almost similar mixing regimes. A typical field batch consisted of 8 m 3 of SCC. This paper addresses areas such as mix design, aggregate grading, system’s water demand, flow and strength of SCC formulations. The results suggest that a thorough understanding of all relevant aspects is essential for successful SCC production. A simple procedure to determine the water demand of a typical SCC formulation is also suggested and is contained in this paper.