scholarly journals Time for concrete casting: a new paradigm

2012 ◽  
Vol 5 (6) ◽  
pp. 798-811
Author(s):  
A. B. Rohden ◽  
D. C. C. Dal Molin ◽  
G. L. Vieira
Keyword(s):  
Compressive Strength ◽  
Test Piece ◽  
Setting Time ◽  
New Paradigm ◽  
Concrete Mixtures ◽  
Concrete Casting ◽  
Brazilian Standard

The Brazilian standard NBR 7212 states that the time of transporting the concrete between the start of mixing should be less than 90 minutes so that by the end of the discharge is a maximum of 150 minutes. Yet often, in construction, concrete is used after this period. In order to investigate the behavior of concrete after setting time of cement was cast six concrete mixtures with two types of cement. The mixtures were produced and kept fresh for six hours, adopting a procedure for maintenance of abatement by superplasticizer and agitation. The results show that of the test piece molded over six hours of maintained or increased the compressive strength average.

scholarly journals Effect of Calcium Nitrate on the Properties of Portland–Limestone Cement-Based Concrete Cured at Low Temperature

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1611
Author(s):  
Gintautas Skripkiūnas ◽  
Asta Kičaitė ◽  
Harald Justnes ◽  
Ina Pundienė
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Setting Time ◽  
Calcium Nitrate ◽  
Curing Temperature ◽  
Hardened Concrete ◽  
Cement Pastes ◽  
Initial Setting Time ◽  
Initial Setting ◽  
Early Strength

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

scholarly journals Effect of Waste Glass on the Properties and Microstructure of Magnesium Potassium Phosphate Cement

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2073
Author(s):  
Qiubai Deng ◽  
Zhenyu Lai ◽  
Rui Xiao ◽  
Jie Wu ◽  
Mengliang Liu ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Glass Powder ◽  
Setting Time ◽  
Potassium Phosphate ◽  
Heat Of Hydration ◽  
Waste Glass ◽  
Hydration Heat ◽  
Magnesium Potassium Phosphate Cement ◽  
The Matrix ◽  
Powder Content

Waste glass is a bulk solid waste, and its utilization is of great consequence for environmental protection; the application of waste glass to magnesium phosphate cement can also play a prominent role in its recycling. The purpose of this study is to evaluate the effect of glass powder (GP) on the mechanical and working properties of magnesium potassium phosphate cement (MKPC). Moreover, a 40mm × 40mm × 40mm mold was used in this experiment, the workability, setting time, strength, hydration heat release, porosity, and microstructure of the specimens were evaluated. The results indicated that the addition of glass powder prolonged the setting time of MKPC, reduced the workability of the matrix, and effectively lowered the hydration heat of the MKPC. Compared to an M/P ratio (MgO/KH2PO4 mass ratio) of 1:1, the workability of the MKPC with M/P ratios of 2:1 and 3:1 was reduced by 1% and 2.1%, respectively, and the peak hydration temperatures were reduced by 0.5% and 14.6%, respectively. The compressive strength of MKPC increased with an increase in the glass powder content at the M/P ratio of 1:1, and the addition of glass powder reduced the porosity of the matrix, effectively increased the yield of struvite-K, and affected the morphology of the hydration products. With an increase in the M/P ratio, the struvite-K content decreased, many tiny pores were more prevalent on the surface of the matrix, and the bonding integrity between the MKPC was weakened, thereby reducing the compressive strength of the matrix. At less than 40 wt.% glass powder content, the performance of MKPC improved at an M/P ratio of 1:1. In general, the addition of glass powders improved the mechanical properties of MKPC and reduced the heat of hydration.

scholarly journals Cement-Based Renders Manufactured with Phase-Change Materials: Applications and Feasibility

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Luigi Coppola ◽  
Denny Coffetti ◽  
Sergio Lorenzi
Keyword(s):  
Compressive Strength ◽  
Phase Change ◽  
Phase Change Materials ◽  
Residential Buildings ◽  
Setting Time ◽  
Drying Shrinkage ◽  
Hydration Kinetics ◽  
Mechanical Performances ◽  
Entrapped Air ◽  
Kinetics Of

The paper focuses on the evaluation of the rheological and mechanical performances of cement-based renders manufactured with phase-change materials (PCM) in form of microencapsulated paraffin for innovative and ecofriendly residential buildings. Specifically, cement-based renders were manufactured by incorporating different amount of paraffin microcapsules—ranging from 5% to 20% by weight with respect to binder. Specific mass, entrained or entrapped air, and setting time were evaluated on fresh mortars. Compressive strength was measured over time to evaluate the effect of the PCM addition on the hydration kinetics of cement. Drying shrinkage was also evaluated. Experimental results confirmed that the compressive strength decreases as the amount of PCM increases. Furthermore, the higher the PCM content, the higher the drying shrinkage. The results confirm the possibility of manufacturing cement-based renders containing up to 20% by weight of PCM microcapsules with respect to binder.

scholarly journals Enhancing the mechanical properties and cytocompatibility of magnesium potassium phosphate cement by incorporating oxygen-carboxymethyl chitosan

2020 ◽  
Author(s):  
Changtian Gong ◽  
Shuo Fang ◽  
Kezhou Xia ◽  
Jingteng Chen ◽  
Liangyu Guo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Physicochemical Properties ◽  
Bone Cement ◽  
Ph Value ◽  
Setting Time ◽  
Potassium Phosphate ◽  
Carboxymethyl Chitosan ◽  
Bioactive Substances ◽  
Magnesium Potassium Phosphate Cement

Abstract Incorporating bioactive substances into synthetic bioceramic scaffolds is challenging. In this work, oxygen-carboxymethyl chitosan (O-CMC), a natural biopolymer that is nontoxic, biodegradable and biocompatible, was introduced into magnesium potassium phosphate cement (K-struvite) to enhance its mechanical properties and cytocompatibility. This study aimed to develop O-CMC/magnesium potassium phosphate composite bone cement (OMPC), thereby combining the optimum bioactivity of O-CMC with the extraordinary self-setting properties and mechanical intensity of the K-struvite. Our results indicated that O-CMC incorporation increased the compressive strength and setting time of K-struvite and decreased its porosity and pH value. Furthermore, OMPC scaffolds remarkably improved the proliferation, adhesion and osteogenesis related differentiation of MC3T3-E1 cells. Therefore, O-CMC introduced suitable physicochemical properties to K-struvite and enhanced its cytocompatibility for use in bone regeneration.

scholarly journals The Effect of Recycled HDPE Plastic Additions on Concrete Performance

Recycling ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 18
Author(s):  
Tamrin ◽  
Juli Nurdiana
Keyword(s):  
Compressive Strength ◽  
High Density Polyethylene ◽  
Concrete Mixtures ◽  
Best Response ◽  
Structural Applications ◽  
Optimal Mix ◽  
Increased Strength ◽  
Selection Of ◽  
Recycled Hdpe ◽  
Lower Medium

This study examined HDPE (high-density polyethylene) plastic waste as an added material for concrete mixtures. The selection of HDPE was based on its increased strength, hardness, and resistance to high temperatures compared with other plastics. It focused on how HDPE plastic can be used as an additive in concrete to increase its tensile strength and compressive strength. 156 specimens were used to identify the effect of adding different percentages and sizes of HDPE lamellar particles to lower, medium, and higher strength concrete for non-structural applications. HDPE 0.5 mm thick lamellar particles with sizes of 10 × 10 mm, 5 × 20 mm, and 2.5 × 40 mm were added at 2.5%, 5%, 10%, and 20% by weight of cement. The results showed that the medium concrete class (with compressive strength equal to 10 MPa) had the best response to the addition of HDPE. The 5% HDPE addition represented the optimal mix for all concrete types, while the 5 × 20 mm size was best.

Treated Effluent in Concrete Technology

2012 ◽  
Author(s):  
Soon Lee Ooi ◽  
Mohd Razman Salim ◽  
Mohammad Ismail ◽  
Md. Imtiaj Ali
Keyword(s):  
Compressive Strength ◽  
Potable Water ◽  
Setting Time ◽  
Sewage Treatment ◽  
Concrete Technology ◽  
Water Quality Control ◽  
Treated Effluent ◽  
Compressive Strength Test ◽  
Direct Discharge ◽  
Mixing Water

In this paper, the feasibility of using treated effluent for concrete mixing was studied. Treated effluent from sewage treatment plants in Malaysia is currently being wasted through direct discharge into waterways. With proper water quality control, this treated effluent can also be considered as a potential water resource for specific applications. Two tests were carried out namely compressive strength test and setting time to determine the feasibility of using treated effluent for concrete mixing. The results were compared against the test conducted on control specimens which used potable water. The results showed that treated effluent increases the compressive strength and setting time when compared with potable water. Key words: treated effluent; mixing water; compressive strength; setting time; concrete technology.

Effects of the addition of nanoparticulate calcium carbonate on setting time, dimensional change, compressive strength, solubility and pH of MTA

2016 ◽  
Vol 50 (1) ◽  
pp. 97-105 ◽  
Author(s):  
A. Bernardi ◽  
E. A. Bortoluzzi ◽  
W. T. Felippe ◽  
M. C. S. Felippe ◽  
W. S. Wan ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Calcium Carbonate ◽  
Setting Time ◽  
Dimensional Change
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