Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

395

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

MITIGATION OF EARLY AGE SHRINKAGE OF UHPFRC BY USING 

SPENT EQUILIBRIUM CATALYST 

 

Ana Mafalda Matos 

(1)

, Sandra Nunes 

(1)

, Carla Costa 

(2)

 

 

(1) CONSTRUCT-LABEST, Faculty of Engineering (FEUP), University of Porto, Portugal  

(2) Department of Civil Engineering, High Institute of Engineering of Lisbon (ISEL), 

Portugal  

 

 

 

 

 

Abstract 

Strengthening of structural concrete elements with ultra-high performance fibre reinforced 

composites (UHPFRC) layers is being successfully performed in recent years. The main 

advantage of UHPFRC in this context is that it can play a double function (water tightness 

and strengthening), while enabling short-time interventions.  

UHPFRC material exhibits remarkable mechanical properties namely, strain hardening in 

tension and extremely low water permeability. However, due to the very low water/binder 

ratio it is prone to autogenous shrinkage. The restraint provided by the substrate to the free 

shrinkage of the new layer generates built-in stresses which can impair its performance. As 

such, seeking strategies to reduce the autogenous shrinkage is an objective to pursue.  

The spent equilibrium catalyst (ECat) is a waste generated by the oil refinery industry with 

very high pozzolanic activity and high specific surface (150 m

2

/g) which promotes a 

significant water absorption (about 30%, by mass), thus has a great potential to work as an 

internal curing agent in UHPFRC. Within this scope, this paper describes research on the 

viability of using ECat to mitigate autogenous shrinkage of UHPFRC. Test results showed a 

significant reduction of autogenous shrinkage in UHPFRC mortars without fibres and 20% 

and 30% of sand replacement by ECat.   

 

 

1. Introduction 

 

Nowadays, performance assessment of concrete mixtures is not limited to workability and 

compressive strength testing. Due to the growing relevance of life cycle cost analysis, the 

durability issues are of primordial importance within the aim of evaluating the suitability of a 

concrete mixture or constituent [1]. 

Ultra-high performance fibre reinforced composites (UHPFRC) - which have been developed 

recently - exhibits remarkable mechanical properties (compressive strength >150 MPa and 

tensile strengths of 10-20 MPa), notably strain hardening in tension (3-10 ‰) and extremely 

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396

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

low water permeability. Strengthening of structural concrete elements with UHPFRC layers is 

being successfully performed in recent years. The main advantage of UHPFRC in this context 

is that it can play a double function (water tightness and strengthening), while enabling short-

time interventions. However, due to its low water–binder ratio and high-fineness additives 

without any coarse aggregate it is prone to exhibit high autogenous shrinkage deformations.  

When a layer of fresh mortar or concrete is applied over an existing concrete the restriction 

conferred by the substrate to the new layer deformation generates internal tensile stresses. The 

magnitude of these internal stresses, which can result in premature cracks, depends on the 

development of material properties during early ages, namely, the magnitude and evolution of 

shrinkage, tensile creep and the evolution of the young´s modulus of elasticity. If 

conventional concretes/mortars are used these internal tensions often lead to cracking, making 

the intervention ineffective. Since UHPFRC exhibits significant strain hardening behaviour in 

tension is more suitable for these applications because only very fine microcracks can occur, 

without compromising the impermeability of the material. Nevertheless, in zones with poor 

fibre distribution or orientation larger cracks might occur in the UHPFRC layer, impairing the 

long-term performance of UHPFRC. Thus, attempts have been made to mitigate the 

autogenous shrinkage of UHPFRC. 

Both, external curing and internal curing are two potential approaches to pursue the 

aforementioned goal. However, it has been reported that external curing is not effective 

enough to mitigate the autogenous shrinkage of UHPFRC because its microstructure is so 

dense that the external water has difficulties to penetrate into the concrete [2], [3]. As such, 

internal curing seems to be a more effective method to mitigate the autogenous shrinkage for 

UHPFRC. Currently, superabsorbent polymers (SAP) are the most popular internal curing 

agents [4]-[6]. SAP possible disadvantages are that they may destabilize the air void system 

(leaving voids larger than 600  m in concrete matrix [2], [7], [8]), retard the hydration 

reactions (increasing the setting time) and reduce the strength [3], [6], [8]-[10]. In addition, 

the number of practical applications is limited due to the high costs involved [11]. In an 

attempt to overcome these disadvantages, this work fosters the assessment of a waste 

generated by the oil refinery industry - namely, the spent equilibrium catalyst (ECat) - as 

internal curing agent. 

The equilibrium catalyst is used in Fluid Catalytic Cracking (FCC) unit during the cracking 

process to convert heavy oils into more valuable gasoline and lighter products. Since, during 

the FCC process, the catalyst active sites are deactivated it undergoes rigorous thermal 

treatments. Nevertheless, after several regeneration cycles it loses its catalytic activity and has 

to be removed from the process giving rise to a waste [12] which is mainly disposal of in 

landfills. Every year the worldwide ECat supply is estimated at about 840,000 tonnes [13]. 

This amount of ECat can be easily used by incorporating in concrete, as the 2014 world 

cement production was 4.3 billion tonnes [14]. Chemically, the ECat is essentially an 

aluminosilicate which main active phase is Y-zeolite, a crystalline aluminossilicate with a 

structure consisting of tunnels and cages that leads to a high (internal and external) surface 

specfic area. The exact composition of these catalysts depends on the manufacturer and on the 

oil refining process that is going to be used. 

Therefore, due to its aluminosilicate chemical composition, ECat has a potential pozzolanic 

activity confirmed in the bibliography [15]-[23], hence, is likely to be use as cement-based 

material additive. In this use, ECat may contributes to accelerate the hydration and the setting 

process [18] as well as to increase the compressive and flexural strengths [1], [15], [18], [20], 

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