Cement substitution by a recycled cement paste fine: Role of the residual anhydrous clinker

Published Date
1 February 2017, Vol.132:1–8, doi:10.1016/j.conbuildmat.2016.11.080

Author 

Arthur Bordy ^a,

Akli Younsi ^b,

Salima Aggoun ^a,,

Bruno Fiorio ^a,

aUniversity of Cergy-Pontoise, L2MGC, 5 Mail Gay-Lussac, 95031 Cergy-Pontoise Cedex, France

bUniversity of La Rochelle, CNRS, LaSIE, UMR-7356, Avenue Michel Crépeau, 17042 La Rochelle Cedex 1, France

Received 23 August 2016. Revised 2 November 2016. Accepted 15 November 2016. Available online 1 December 2016. 

Highlights

• RCPF just fills the granular gap left by the substituted cement in mortar mixtures.
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  RCPF contains around 24% of a reactive residual anhydrous clinker.
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  RCPF contributes in the hydration process through its anhydrous clinker.
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  RCPF contributes in the mechanical properties through its anhydrous clinker.
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  RCPF contributes in the carbonation resistance through its anhydrous clinker.

Abstract

This paper reports on an experimental study conducted on mortars designed with substitution of Portland cement by a recycled cement paste fine (RCPF) obtained from crushing, grinding and 80-μm sieving of a laboratory-made cement paste. The obtained results show that in terms of fineness, particle size distribution, CaCO₃content, hydration kinetics, total porosity and mechanical properties, the use of RCPF as partial substitution of cement should not provide any additional filler effect and nucleation sites compared to the replaced cement. The results show also that RCPF contains around 24% of a reactive residual anhydrous clinker which contributes in the hydration process, the mechanical properties and the resistance against carbonation.

Keywords

Portland cement

Cement paste

Recycled cement paste fine

Anhydrous clinker

Mortar mixture

Hydration temperature

Portlandite content

Total porosity

Compressive strength

Carbonation depth

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• ⁎ 
  Corresponding author.
  
  

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Evaluation of the impact of corrosion of hot-dip galvanized reinforcement on bond strength with concrete – A review

Published Date
1 February 2017, Vol.132:271–289, doi:10.1016/j.conbuildmat.2016.11.096

Review

Author

Petr Pokorný ^a,,

Petr Tej ^a

Milan Kouřil ^b

• aKlokner Institute, Czech Technical University in Prague, Prague, Czech Republic
• bUniversity of Chemistry and Technology Prague, Prague, Czech Republic

Received 30 December 2015. Revised 12 October 2016. Accepted 20 November 2016. Available online 9 December 2016. 

Highlights

• This review article describes in detail the impact of corrosion of hot-dip galvanized steel on bond strength with concrete.
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  This work focuses on the influence of all aspects (not only corrosion induced aspects) of the development of bond between hot-dip galvanized steel and concrete.
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  To evaluate the extent of effective corrosion protection, investigations evaluating the corrosion behavior of galvanized steel in fresh and hardening concrete must be re-opened.

Abstract

This review focuses on the effect of initial corrosion of hot-dip galvanized reinforcement in both fresh and curing concrete on total bond strength.

Corrosion behavior of hot-dip galvanized steel is studied in detail in both alkaline solutions without calcium cations and model pore solutions (with Ca²⁺). Relation between pH and resulting extent of corrosion attack on coating is also discussed. The effect of top layer of coating, consisting of various intermetallic phases on corrosion resistance is also discussed.

Regarding the standardized bond strength test procedures, the effects of hydrogen evolution on porosity of adjacent cement and bond strength of galvanized steel and concrete were analyzed. Negative effect of zinc corrosion products is described – concrete curing and hardening of concrete is retarded in their presence, their growth can cause local disintegration.

Close attention is also given to eventual surface modification of galvanized reinforcement aimed at reducing the negative effect of reinforcement corrosion on bond strength (chromate, phosphate, organosilane and other coatings).

The review points out many contradicting results and therefore the fact that real consequences of galvanized reinforcement corrosion are not, even at present day, known. Use of galvanized zinc coatings for protection of conventional steel reinforcement cannot, to this day, be considered clearly beneficial and research regarding the topic to be finished.

Keywords

Corrosion steel in concrete

Epoxy coated reinforcement

Hot-dip galvanized reinforcement

Fe–Zn intermetallics

Bond strength

Pull-out test

Beam test

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• ⁎ 
  Corresponding author.
  
  

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061816318657

Potential of rice husk ash for mitigating the alkali-silica reaction in mortar bars incorporating reactive aggregates

Published Date
1 February 2017, Vol.132:61–70, doi:10.1016/j.conbuildmat.2016.11.126

Author 

 Abbas ^a,,

Syed M.S. Kazmi ^b

Muhammad J. Munir ^b

aDepartment of Civil Engineering, University of Engineering and Technology, Lahore, Pakistan

bDepartment of Civil Engineering, Mirpur University of Science and Technology, Mirpur, AJK, Pakistan

Received 26 July 2016. Revised 21 November 2016. Accepted 26 November 2016. Available online 2 December 2016. 

Highlights

• Effect of RHA in mitigating the ASR expansion was investigated.
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  SEM and EDS analysis were conducted to study the micro-structural behavior due to ASR.
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  Incorporating RHA as a pozzolan can be helpful for mitigating the ASR expansion.

Abstract

Alkali-silica reaction (ASR) in concrete structures is very common problem around the globe. In this study, the potential of rice husk ash (RHA) in mitigating the ASR expansion was investigated. For this purpose, aggregates from reactive source were selected. RHA was acquired from local industry. Mortar bar specimens were prepared with various RHA proportions (10%, 20%, 30% and 40% by cement weight) to evaluate the ASR expansion in accordance with ASTM C1260. The pozzolanic reactivity of RHA was also evaluated using strength activity index and thermal analysis. Results showed satisfactory level of pozzolanic reactivity when cement was partially replaced with RHA. Mortar bars expansion results showed 23% and 50% decrease in expansion for specimen incorporating 10% and 40% of RHA, respectively. Scanning electron microscopy (SEM) also showed cracking due to ASR in control specimens; however, no cracks were observed in mortar bar specimens incorporating RHA. Moreover, energy disperse X-ray spectroscopy (EDS) analysis of mortar bars incorporating RHA showed low calcium to silica ratio with higher amount of alumina which may resulted into alkali reduction due to alkali absorption and dilution process leading to reduce the ASR expansion. Therefore, the incorporation of RHA as a pozzolanic material can be helpful in binding alkalies and mitigating the ASR expansion.

Keywords

Rice husk ash

Alkali-silica reaction

Mortar bars expansion

Activity index

Thermal analysis

Microscopic examination

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• ⁎ 
  Corresponding author.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061816318955