Performance Evaluation and Research of Versatile Cement Mortar with Rapid Strength Increase Academic research paper on "Agriculture, forestry, and fisheries"

Procedia Engineering

www.elsevier.com/locate/procedia

18th International Conference on Rehabilitation and Reconstruction of Buildings 2016, CRRB

Performance Evaluation and Research of Versatile Cement Mortar

with Rapid Strength Increase

Rostislav Dochytkaa, Vit Cernya, Michaela Dvorakovaa*

aBrno University of Technology, Faculty of Civil Engineering, Veven 331/95, 602 00, Brno, Czech Republic66

Abstract

Portland cement concrete is the world's most versatile and most used construction material. In order to meet the global demand for sustainability, civil engineers have looked to alternative supplementary cementitious materials (SCMs) such as fly ash to increase durability while lowering the initial and life-cycle cost. The objective of this study was to characterize the hardened concrete characteristics of cementitious compositions. Mechanical properties are the most important properties of hardened cementitious materials (cementitious materials with partial substitution by fly ash), therefore the research was primarily focused on compressive and tensile strength, bulk density, wear resistance and resistance against chemical environments.

©2017 The Authors.Publishedby Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-reviewunderresponsibilityofthe organizingcommitteeofthe 18thInternationalConferenceonRehabilitationand ReconstructionofBuildings2016

Keywords: Fly ash; secondary raw material; cement mortat, mechanical properties

1. Introduction

Fly ash, by-product of the coal-fired power plants is well accepted as a pozzolanic material that may be used as a mineral admixture in concrete. Positive affect of fly ash on hydration, reduction of porosity and thus decreasing of diffusion of CO2 depending on its chemical composition and origin have been tested in recent years [1] - [4].

CrossMark

Available online at www.sciencedirect.com

ScienceDirect

Procedia Engineering 195 (2017) 228 - 235

* Corresponding author. Tel.: +420-541-147-225; fax: +420-541-147-502. E-mail address: dvorakova.m@fce.vutbr.cz

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the 18 th International Conference on Rehabilitation and Reconstruction of Buildings 2016 doi:10.1016/j.proeng.2017.04.548

Utilization of fly ash has both positive ecological aspect (utilization of secondary raw material instead of landfilling, the reduction of cement use and subsequently of CO2 emissions) and economical aspect (reduced price of final material due to the reduction of cement) [2]. Many studies have shown that the replacement of cement by fly ash improves the workability, reduces hydration heat, reduce the rate and amount of bleeding due to the reduced water demand and helps in the development of long term compressive strength (at ages > 90 days) [6] - [7]. The impact of fly ash is dependent not only on the composition and quantity of fly ash used, but also on type and amount of cement, water-cement ratio (w/cm), the type and amount of chemical admixtures and the concrete temperature.

Trend of modern times is to optimize the construction time to necessary minimum. Reconstruction and rehabilitation of existing buildings require shorter or longer shutdowns that could negatively affect the existence of operation (slowing or stopping of production or services, which may lead to loss of profit or customers). Current state of the object can lead to the question: "repair or remove"? A restoration project using the correct repair products can add years to the service life of a structure. The cost to properly repair a structure is often significantly less than the cost of replacement or further deterioration. However, a poorly designed repair project using the unsuitable materials can result in a continuing, expensive process.

2. Experimental study

2.1. Materials and formulations

Based on a previously carried out experimental studies [1] - [4] various mix proportion of cement based mortar with addition of 20% of fly ash from location Tusimice (formula 20%ETU), Opatovice (formula 20%EPO) and Pocerady (formula 20%EPC) were prepared. Mix design is given in Table 1 and formulas composition is given in Table 2.

Further a reference formula was prepared and tested for the comparison, i.e. without any secondary raw additives (formula REF). Specimens of dimensions (40x40x160) mm3 were curing in wet conditions for 5 days and then in laboratory ambient for 23 days. Quartz sand of fraction 0-4 mm and Portland cement CEM I were selected.

Table 1. Mix design of the versatile cement mortars

Dosage

Component

from - to (%)

Portland cement CEM I 35 40

Aggregate 4/8 mm 12 16

Quartz sand 0,1 - 0,6 mm 6 10

Quartz sand 0,6 - 1,0 mm 6 10

Quartz sand 1,0 - 4,0 mm 10 15

Fine particles of limestone 3 5

Polypropylene fibres 0,04 0,06

Micro-silica 1,5 1,8

Calcium aluminate cement 9 14

Pozzolanic additive 1,5 2,0

Antifoaming additive 0,2 0,3

Superplasticizer 0,5 0,8

Decelerating additive 0,4 0,7

Table 2. Composition of formulas

Indication Dosage of fly ash (%) Location of fly ash production

REF 0 Reference

20%_EPO 20 Opatovice

20%_ETU 20 Tusimice

20%_EPC 20 Pocerady

2.2. Properties of used fly ash

Fly ashes were selected based on the production stability and the similarity of the chemical composition (chemical composition is given in Table 3). Other significant parameter of the ash is particle size distribution given in Fig. 1.

Table 3. Chemical composition of fly ashes

Location of fly ash production SiO2 AL2O3 Fe2Os SO3 CaO MgO K2O Na2O P2O5

Opatovice 52,5 26,5 6,05 0,05 1,38 0,94 1,69 0,32 0,12

Tusimice 50,0 23,4 14,50 0,26 3,42 1,72 1,07 0,29 0,16

Pocerady 54,6 29,5 5,46 0,08 1,81 0,96 1,34 0,25 0,11

Fig. 1. Particle size distribution of fly ash (a) ETU Tusimice; b) EPO Opatovice; c) EPC Pocerady)

3. Experimental methods

Mechanical properties are the most important properties of hardened cementitious materials (cementitious materials with partial substitution by fly ash), therefore the research was primary focus on compressive and tensile

Partide Size fum)

strength, wear resistance - Böhme, bulk density, resistance against chemicals environments and microstructure.

3.1. Flexural strength and compressive strength

Determination of compressive and flexural strength was performed according to the standard EN 13892-2 [8]. To determine the compressive strength, fragments of beams used within the testing of flexural strength were used. For determination of compressive strength steel loading plates with an area of 400 mm2 were put on the top and the bottom of the specimens. Compressive and flexural strength was measured 2, 4, 6 and 24 hour after casting to determine increase of initial strengths. Subsequently the strength was determined by the age of 3, 7, 14 and 28 days.

3.2. Wear resistance - Böhme

To determine the wear resistance according to the standard EN 13892-3 [9] the Böhme abrasion tester was used. Normalised abrasive was spread on the test track and the specimen was positioned in the Böhme abrasion tester. The test was performed for 16 cycles composed of 22 turns each. At the end of the test, the wear was calculated as an average loss in volume and weight.

3.3. Bulk density

The bulk density is the apparent bulk density of the hardened specimens at the age of 28 days. The determination of the bulk density was performed in accordance with the standard EN 206 [10].

3.4. Flexural strength and compressive strength

Determination of compressive and flexural strength after 2 months exposition in chemicals environment was performed according to the standard EN 13892-2 [8]. Compressive and flexural strength was measured by the age of 90 days (specimens of the age of 28 days were exposed to chemicals environment for 2 months).

4. Results of experiments

Fig. 2 shows the compressive strengths and their changes depending on the dosage and type of fly ash within tested period. Tested cement mortar reaches 50 % of the final compressive strength in 24 hours after production. Reference sample reach the lowest compressive strength at the age of 28 days (fc28). A significant increase in compressive strength (fc28) was observed in case of mix design with addition 20% of fly ash from location Pocerady (20%EPC). The most important finding is that the mortar both with and without fly ash addition reached compressive strength over 20 MPa two hours after casting. Within 3 days the mortar reaches 80% of its final strength and therefore is suitable for special application such as reconstruction and rehabilitation of concrete floors in plants and buildings without the possibility of long shutdowns.

Fig. 2. Compressive strength depending on the dosage and type of fly ash determined after 28 days

Fig. 3 shows the tensile strengths and their changes depending on the dosage and type of fly ash within tested period. Tested cement mortar reaches 90 % of the final compressive strength in the age of 6 hours. Reference sample become clearly the highest tensile strength at every tested stage except final tensile strength ft28 (mix design with 20% of fly ash from location Pocerady (20%EPC) reached tensile strength 7 % higher).

Fig. 3. Tensile strength depending on the dosage and type of fly ash determined after 28 days

Based on the assumption that addition of fly ash improves the resistance to aggressive environments, tested specimens were exposed to H2SO4, diesel fuel and detergent. The aggressive medium were selected based on the possible exposure in practise (diesel fuel - concrete road, concrete floors in parking house, gas station; H2SO4 - acid rains, atmosphere, wastewater; detergent - cleaning products used on concrete floor in halls, parking lots, warehouses etc.)

Fig. 4. Compressive strength determined after two months of exposition to chemical environment

Fig. 5 shows wear resistance according Böhme depending on the dosage and type of fly ash determined after 28 days. It is clear that fly ash in addition of 20 % does not influence abrasion on positive way. Mix design with 20 % of fly ash from location Pocerady (20%EPC) proved 20 % lower wear resistance in comparison with reference sample (REF).

Fig. 5. Wear resistance according Bohme depending on the dosage and type of fly ash determined after 28 days

Fig. 6. Bulk density depending on the dosage and type of fly ash determined after 28 days

5. Conclusion

The main aim of the research was to develop versatile high performance cement based mortar with partial substitution of cement by local fly ash. Cement based mortar with 20 % of fly ash stand out among rapid initial strength increase both compressive and tensile. The most important finding is that the mortar both with and without fly ash addition reached compressive strength over 20 MPa two hours after casting. It can be concluded that construction made of this versatile mortar is walkable and fully operational two hours after manufacturing.

The following conclusion may be drawn from this study:

• Tested cement mortar reaches 50 % of the final compressive strength in 24 hours after production.

• The addition of fly ash in dosage of 20 % does not influence short term compressive and tensile strength in negative way.

• The addition of fly ash in dosage of 20 % does not improve the wear resistance.

• The addition of fly ash has influenced development of hydration heat about 15 %.

• The influence of fly ash addition on chemical resistance was not found.

Acknowledgements

This work was financially supported by the project Standard specific research FAST-S-16-3274 "Research and development of advanced materials for industrial floors".

References

[1] A. Petcherdchoo: Repairs by fly ash concrete to extend service life of chloride-exposed concrete structures considering environmental impacts, Construction and Building Materials, Volume 98, 15 November 2015, Pages 799-809

[2] N. Chousidisa, E. Rakantaa, I. Ioannoub, G. Batisa: Mechanical properties and durability performance of reinforced concrete containing fly ash, Construction and Building Materials, Volume 101, Part 1, 30 December 2015, Pages 810-817

[3] S. Mengxiao, W.Qiang, Z. Zhikai: Comparison of the properties between high-volume fly ash concrete and high-volume steel slag concrete under temperature matching curing condition, Construction and Building Materials, Volume 98, 15 November 2015, Pages 649-655

[4] M. Jalal , A. Pouladkhan , O. F. Harandi , D. Jafari: Comparative study on effects of Class F fly ash, nano silica and silica fume on properties of high performance self compacting concrete, Construction and Building Materials, Volume 94, 30 September 2015, Pages 90-104

[5] M. Fiedlerova, R. Drochytka, P. Dohnalek: Utilization of Fly Ash in High Performance Floor Screed Based on Cement and its Influence on Physical Mechanical Properties. In Binders, Materials and Technologies in Modern Construction II. Materials Science Forum, Volume 865, 11 August 2016., Pages 201-205

[6] Vagelis G. Papadakis: Effect of fly ash on Portland cement systems: Part II. High-calcium fly ash, Construction and Building Materials, Volume 30, 4 August 2010, Pages 1647-1654

[7] Michael Thomas: Optimizing the Use of Fly Ash in Concrete, Portland Cement Association, Publication IS, 548, 2007, 24 pages

[8] European Standard EN 13892-2, Methods of test for screed materials - Part 2: Determination of flexural and compressive strength, 2002

[9] European Standard EN 13892-3, Methods of test for screed materials - Part 3: Determination of wear resistance - Bohme, 2014

[10] European Standard EN 206, Concrete - Specification, performance, production and conformity, 2013