Setting Time Of Cement Paste Research Articles

Properties of High Performance Concrete Containing Waste Glass Micro-Filler

The article discusses possibilities for use fine ground glass obtained from fluorescent lamp utilisation as micro filler in High Performance Concrete (HPC). Investigated mix compositions are based on silica fume (SF) and SF combination with glass powder. Testing results indicates that replacing silica fume by additionally ground fluorescent glass (up to 50%) slightly increasing consumption of water and delaying setting time of cement paste. All HPC mixes with glass powder showing decreased early-age strength and considerable strength gain after long-term hardening. It is concluded, that the best way of glass application in HPC is use fine ground glass powder together with silica fume as complex admixture.

The Mitigation of Alkali-Silica Reactions by Aluminum-Bearing Substances

An ability of aluminum-bearing substances-amorphous aluminum hydroxide, aluminum sulphate and basic aluminum sulphate to mitigate alkali-silica reactions in Portland cement mortars has been studied. At equivalent dosages in terms of Al2O3, these substances are ranged in the following order in respect of inhibiting effect: Al(OH)1.78(SO4)0.61 ≥ Al2(SO4)3 > Al(OH)3. It is found that the plasticizing agents of the main types used in cement compositions have no influence on the inhibiting effect of aluminum-bearing admixtures. To control the setting time of cement paste, iron(II) sulphate may be used for partial substitution of Al2SO4·18H2O, and this operation is not influence on the results of ASR expansion test.

Effect of Partial Replacement of Cement by Hydrated Cement on Properties of Cement Paste and Cement Mortar

This work study the effect of partial replacement of cement by hydrated cement on some properties of cement paste and cement mortar such as normal consistency, initial and final setting time, compressive strength, and length change. The results show that pastes containing hydrated cement require more water than reference paste to give normal consistency. The results also show that the replacement by hydrated cement delay the initial and final setting time of cement paste. The delay in setting time increased with increasing the partial replacement by hydrated cement. Compressive strength test was carried out on (54) cubes of (50) mm side dimensions of mortars containing (5, 10, 15, 20, and 25%) of hydrated cement at (3, 7, and 28) days. They were then compared with reference mortar. The compressive strength results show that the compressive strength decreases with increasing the replacement percentage by hydrated cement at all ages. The decreases in compressive strength reached (23.05 %) when (25%) of cement was replaced by hydrated cement in (28) days. The results also show that the replacement of cement by hydrated cement increases the length change of mortars compared with reference mortar.

Effect of Carboxylmethyl Cellulose Sulfate (CMC-S) on the Hydration Process of Cement Paste

The application of Carboxylmethyl Cellulose Sulfate (CMC-S) in cement paste was studied. The effect of CMC-S on the setting time of cement paste was investigated. Hydration heat of specimens with different cured age was measured via the Hydration Heat Tester (HHT), and hydration process was recorded via Differential Scanning Calorimeter (DSC). The results indicated that CMC-S was a kind of set-retarding and water-reducing agent; its retarding properties appeared at early age, but after three days, the hydration process of cement paste was even improved.

Influence of lithium sulfate addition on the properties of Portland cement paste

Lithium salts are known to have remarkable effect to restrain alkali aggregate reaction, but the influence on strength and setting time of cement paste is uncertain. This paper presents an experimental approach to study the influence of lithium sulfate on strength and setting time of ordinary Portland cement paste with electrical resistivity measurement and other methods. It is shown that lithium sulfate has the function to accelerate cement hydration reaction, shorten setting time and enhance the strength whether at early age or long-term age as well. Meanwhile, the electrical resistivity development of different samples with various dosages of lithium sulfate reflects that lithium sulfate plays the role of set accelerator and hardening accelerator in ordinary Portland cement paste, and the larger content results in stronger effect. So moderate lithium sulfate is beneficial to adjust setting time and increase early strength as well as long-term strength.

Fresh and Hardened Properties of Sustainable Concrete Using Recycled Household Greywater

This study investigates the production of sustainable concrete mixes using recycled household greywater. Batches consisting of different mixes of cement pastes, mortar specimens, and concrete specimens were produced and tested for both fresh and hardened properties. The main variable was the type of water used for mixing and curing. The study showed that the use of greywater had little or no effect on the setting times of cement pastes, while the average workability of fresh concrete was slightly increased. The study also showed that the compressive strength of sustainable concrete was within 90 % of the standard control mix. Generally speaking, the combined results of compressive strength, splitting strength and drying shrinkage of the batches cured using greywater and mixed with either potable or greywater were within acceptable limits, provided that greywater conforms to the limits imposed by the applicable Codes and Standards typically imposed on potable water used in concrete.

Monitoring the evolution of material structure in cement pastes and concretes using electrical property measurements

Electrical conductivity is an effective parameter to monitor the microstructural features of cement-based materials. Monitoring the early age hydration process in cementitious materials containing mineral and chemical admixtures, and non-invasive determination of the pore structure features, through the use of electrical response, is discussed in this paper. The initial and final setting times of cement pastes predicted using electrical property based methods are very close to the measured values, showing that conductivity is an effective tool to monitor the setting process in plain and modified systems. The evolution of total porosity in the selected cement paste and concrete systems is predicted using electrical property based models derived from effective medium and percolation theories, and is found to match well with the experimental values.

Effect of Fly Ash and nanoCaCO<sub>3</sub> on the Setting Time of Cement Paste

This paper presents an experimental study to evaluate the effects of fly ash and nanoCaCO3 on setting time of cement paste. The test group included the contents of fly ash was 30%, 40%, 50%, 60% and content of nanoCaCO3 was 2.5%, 5%, 10%, 20%. Results indicate that setting time was increased with the incorporation of fly ash, shortened with the incorporation of nanoCaCO3. The incorporation of 5% nanoCaCO3 by mass of cementitious materials reduced initial and final setting times by 60 and 70 min, respectively. In comparison to the referenced paste with 40% fly ash. The best fly ash content appear to be 40% when nanoCaCO3 was added.

Effect of low dosages of waste GRP dust on fresh and hardened properties of mortars: Part 1

The viability of improving some durability aspects of mortars through the addition of low dosages of very fine Glass Reinforced Plastic by-product was investigated. Replacing 5–10% of sand volume with GRP dust delays the setting time of cement paste, but the delay can be partially recovered by adopting a previously thermally treated GRP dust. GRP dust increases the workability, autogeneous shrinkage, deformability and total porosity of mortars, though with a smaller average radius. It significantly reduces the mechanical performance of mortars when wet curing conditions are adopted. However, the risk of cracking induced by restrained shrinkage and capillary water absorption is lower in the presence of GRP dust. This decrease could imply enhanced durability of GRP mortars when used as supporting role.

Mechanical Properties of Cement Mortar Containing Fine-Grained Fraction of Fly Ashes

This paper presents the effect of fly ash grain-size fractions on Portland-fly ash cement hydration and its properties. Siliceous fly ashes of size fraction of 0 - 16 and 16 - 32 μm, separated from initial fly ash samples from 1st, 2nd and 3rd hopper in ESP system, were analysed. Cement hydration was investigated by determination of hydration heat and content of Ca(OH)2 and C3S in cement samples. Water to cement ratio and initial setting time of cement pastes as well as compressive strength and microstructure of cement mortars were also analyzed. Results showed that the same amount of the same size ash fraction can give cement of lower or higher early strength and its lower or higher increase with time. Incorporation of 20 wt% of ash fraction of 0 - 16 μm can produce Portland-fly ash cement CEM II/A-V of strength class 42.5R (from 2nd hopper) or 52.5N (from 3rd hopper). Cement containing 40 wt% of ash fraction of 0 - 16 μm from 2nd and 3rd hopper can be classified as pozzolanic cements CEM IV/A-V of strength class 42.5 and normal or rapid early strength, respectively. Different development of strength of cement with addition of the same size ash fraction separated from the initial ash sample from the next hopper in ESP system is connected with higher depolymerization degree of SiO4 units in ash glass, resulting from the greater amount of AlO4 units replacing SiO4 units. Ash fraction of 16 - 32 μm shows lower depolymerisation of glass network and as a consequence lower hydration degree of C3S to portlandite and calcium silicate hydrates (C-S-H).

Utilization of Steel Slag Powder as a Combined Admixture with Ground Granulated Blast-Furnace Slag in Cement Based Materials

AbstractThe feasibility of steel slag powder as a combined admixture with ground granulated blast-furnace slag (GGBFS) in cement based materials was explored. The effects of steel slag powder on the normal consistency water requirement, setting times, compressive strength, and hydration products of cement paste/mortar were studied. The results showed that the preferred additional content of steel slag powder in a combined admixture was less than 20%. Steel slag powder decreased the normal consistency water requirement and retarded the setting time of cement paste. With curing ages increasing, the compressive strength of mortars with the combined admixture increased rapidly, even higher than that of the blank sample. Hydration products primarily included C-S-H gel, C-S-Al-H gel, and Ca(OH)2. Mixing these two powders of GGBFS and steel slag powder had a positive effect regarding the hydration of steel slag powder. Additionally, this research contributes to our understanding of how to sustainably manage indu...

Prediction of the degree of hydration at initial setting time of cement paste with particle agglomeration

This paper presents a computer simulation method for predicting the degree of hydration at the initial setting time of cement paste with particle agglomeration. Agglomeration is controlled by using a square-well potential for the interaction between two cement particles, and the degree of hydration at the initial setting time is determined using the burning algorithm. It is verified that, when the critical surface-to-surface distance for attachment is taken as 0.05μm, the simulation predictions are in good agreement with experimental results. For cement particles in water at the initial stage of hydration, the number of clusters obeys the power law with an average Fisher exponent of 1.9. Finally, the effects of key factors affecting the degree of hydration at the initial setting time are quantitatively evaluated.

Effect of Structure of Polycarboxylate Superplasticizer on Hydration of Cement in Early Period

Effect of polycarboxylate superplasticizer (PCs) with different bond between side chain and truck chain on hydration of cement in early period was studied. The performance of PCs in concrete was investigated by setting time, TGA and SEM. PC-based superplasticizer with ester bonding between side chain and truck chain. Although they had the proximate structure parameters in density of side chain and absorption group (carboxyl groups), the setting time of cement paste was significantly different when different PCs were employed in the preparation of cement. Decomposing of this bond in alkali environment may lead to a shorter setting time. On the other hand, same difference in hydration production was observed in early period hydration of cement paste when two different PCs was incorporated, which indicated that the different bond structure in PCs affected the hydration of cement in a different manner. The result of SEM indicated that the morphological phase of hydrated product was different when PC was applied, this may be related with the different result in the TG and TGA

Setting Time Measurement Using Ultrasonic Wave Reflection

Ultrasonic shear wave reflection was used to investigate setting times of cement pastes by measuring the reflection coefficient at the interface between hydrating cement pastes of varying water-to-cement ratio and an ultrasonic buffer material. Several different buffer materials were employed, and the choice of buffer was seen to strongly affect measurement sensitivity; high impact polystyrene showed the highest sensitivity to setting processes because it had the lowest acoustic impedance value. The results show that ultrasonic shear-wave reflection can be used successfully to monitor early setting processes of cement paste with good sensitivity when such a very low impedance buffer is employed. Criteria are proposed to define set times, and the resulting initial and final set times agreed broadly with those determined using the standard penetration resistance test.

RECYCLING OF WASTE GLASS IN MORTAR MIXTURES

There is a growing environmental concern in many countries around the world from the accumulation of solid waste glass since not all glass can be recycled into new glass. This study explores the recycling of solid waste glass in concrete mixtures to reduce the environmental pollution and to improve the properties of concrete material. Three waste glass powder (WGP) levels were considered in this study: 5%, 10% and 15%. The properties investigated include: setting time, workability, compressive and flexural strength and micro-structure of mortar. The mortar mixtures proportions were 1:3:0.7 by weight for cement, sand and water, respectively. The results showed that the solid waste glass can be recycled in cement concrete mixtures and improve the properties of concrete. The setting time of cement paste increased and the workability decreased with the increase of the WGP content. The compressive strength of mortar increased with the increase of WGP as partial replacement of limestone sand under moist curing. The flexural strength of mortar increased with the increase of WGP as partial replacement of cement or sand under moist curing. The autoclaved WGP mortar showed higher compressive strength and lower flexural strength compared to the moist cured mortar. The scanning electron microscopy images showed that WGP material is good filler because it reduced the porosity of mortar.

Effects of the Synthetic Ways of Sulfonated-Phenol-Formaldehyde (SPF) Polymers on Application Properties of Cementitious Materials

The water-soluble sulfonated phenol-formaldehyde (SPF) polymer was synthesized at three synthetic way, the molecular structure of SPF-1, SPF-2, SPF-3 polymer was characterized by Gel permeation chromatography (GPC) and infrared spectroscopy (IR), the application properties of cementitious material with SPF-1, SPF-2, SPF-3 polymer were assessed. The experimental results indicate that cement paste with SPF-3 polymer has highest initial fluidity and compressive strength, lowest fluidity loss in SPF-1, SPF-2 and SPF-3 polymer, the effect of SPF-1, SPF-2, SPF-3 polymer on setting times of cement paste has the same laws. SPF-3 polymer synthesized using sulfomethylation way has better application properties on cementitious material.

Stabilisation of medical waste ash in mortar mixtures

This study investigates the stabilisation of medical waste ash (MWA) in mortar mixtures. Three MWA dosages were considered in the study: 5%, 10% and 15%. The other experimental parameters investigated in the study were: aggregate type and curing regime. The properties explored in the study include: setting time, workability, compressive and flexural strength and leaching of heavy metals. The mortar mixture proportions were 1∶3∶0·7 by weight for cement, sand and water, respectively. The results of the study have shown that MWA can be stabilised in mortar mixtures without significant leaching of heavy metals. The setting time of cement paste decreased with the increase in MWA content. The workability of mortar increased when the MWA level was increased. The compressive strength of mortar increased with the increase in the MWA content as a partial replacement of silica sand under moist and autoclaving curing conditions. However, the flexural strength of mortar decreased as the content of MWA increased as a partial replacement of silica sand under moist and autoclaving curing. The amount of heavy metals leached from mortar specimens after 28 days’ immersion in water were very small and insignificant (maximum percentage 0·58%) compared with the original heavy metals present in the MWA powder.

Application of Ultrasonic Measurements for Determination of Setting and Hardening in Cement Paste

Concrete setting and hardening processes are the most critical phases during construction works, influencing properties of a concrete structure. The initial set is important as it provides an estimate when concrete has reached a point that it can no longer be vibrated without damaging concrete. The point at which final set occurs is important since it provides an estimate when the development of concrete strength and stiffness starts. In this study, experimental work is performed under laboratory conditions to indentify the setting time of cement paste using ultrasonic waves. Correlation between the ultrasonic wave parameters (speed, amplitude and energy) passing through the fresh cement paste and setting time determined using the Vicat test method is analyzed. A method of acoustic emission is also used and acoustic signals recorded in cement paste during hydration are presented.

Effect of Side Chains and Sulfonic Groups on the Performance of Polycarboxylate-Type Superplasticizers in Concentrated Cement Suspensions

Polycarboxylate-type superplasticizers (PCs) containing different side chains and sulfonic groups have been synthesized, and the effect of side chains and sulfonic groups on their performance in cementitious systems has been intensively investigated by measuring zeta potential, thickness of absorption layer, paste fluidity, rheological properties as well as the setting time in this paper. Results show that the PC containing both short poly(ethylene oxide) (PEO) side chains and long PEO side chains with the molar ratio of 1:1 has a better dispersibility than the PC containing only short PEO side chains or only long PEO side chains in cement suspensions. The shorter the side chain of the PC, the longer the setting time of cement paste incorporating it. An appropriate increase of sulfonic group content is beneficial for the improvement of dispersibility for the PC and leads to no obvious change for the setting time. It also suggests that there is a geometrical balance between the PEO side chains and sulfonic groups for the performance of PC. This work is not only helpful for understanding the relationship of molecular structure of PCs and their performance, but also further designing optimum molecular structure of PC to meet the requirement in different concrete system.

On the Evaluation of Setting Time of Cement Paste Based on ASTM C403 Penetration Resistance Test

Abstract The standard setting test for setting of cement paste, ASTM C191, uses a very stiff dough with a low water content and does not give information about the gradual microstructural development over time due to hydration; but the standard test for concrete, ASTM C403, can be used on cement paste, is not limited to paste with low water content, and does give information about microstructural development. In this study, the C403 test procedure was modified to provide more reproducible data for cement paste, with the most important modification being to not remove bleed water. Since the purpose of ASTM C403 is to measure time of setting of mortar extracted from concrete, the values of penetration resistance in paste that correspond to initial and final set in concrete were determined: These values were 2 MPa for initial set and 14 MPa for final set.