This paper reports experimental results of 32 hybrid cement mixes regarding the joint effect of sodium hydroxide concentration, the use of a commercial superplasticizer and a biopolymer on the flow and compressive strength performance. The results show that the use of commercial admixtures led to a slightly increase in the flow of mortars with lower sodium hydroxide concentration. A mixture based on 80% fly ash, 10% calcium hydroxide and 10% waste glass showed the highest compressive strength. A compressive strength decrease was noticed concerning the use of the two admixtures that can due to the fact that those admixtures are not stable on high basic media. The authors would like to acknowledge the financial support of
the Foundation for Science and Technology (FCT) in the frame
of project IF/00706/2014-UM.2.15info:eu-repo/semantics/publishedVersio

Abdollahnejad, Zahra

Kheradmand, Mohammad

Pacheco-Torgal, F.

Universidade do Minho: RepositoriUM

     Abstract—. This paper reports experimental results of 32 hybrid cement mixes regarding the joint effect of sodium hydroxide concentration, the use of a commercial superplasticizer and a biopolymer on the flow and compressive strength performance. The results show that the use of commercial admixtures led to a slightly increase in the flow of mortars with lower sodium hydroxide concentration. A mixture based on 80% fly ash, 10% calcium hydroxide and 10% waste glass showed the highest compressive strength. A compressive strength decrease was noticed concerning the use of the two admixtures that can due to the fact that those admixtures are not stable on high basic media.   Keywords—Waste reuse, fly ash, waste glass, hybrid cement, biopolymer, polycarboxylate, flow  I. INTRODUCTION Hybrid cements involve the activation of industrial wastes with alkaline activators, usually composed by hydroxide, silicate, carbonate or sulfate leading to  co-precipitation of two gels (C-S-H + N-A-S-H) [1, 2]. This materials have a particular ability for the reuse of several types of wastes [3, 4]. Therefore the valorization of fly ash and waste glass in hybrid cement would have obvious environmental benefits. Workability is an important engineering property in the construction industry just because lower workability requires higher compaction energy. Alkaline cements usually use viscous activators that are associated with low workability performance. The superplasticizers that are currently used by the Portland cement (OPC) industry show little or even no effect when used on AACB mortars [5]. Others reported a slight improvement on workability but at the expense of a reduction on compressive strength [6,7]. Others showed that the workability depended on the mix design composition [8,9]. More recently Yang et al. [10] noticed that polycarboxylate-based superplasticizer showed a retarding effect on alkali-activated fly ash/slag mistures. Therefore, the purpose of this paper is to understand how the composition of hybrid cements based on fly ash and waste soda lime silicate glass and two commercial superplasticizers influences its workability and also its mechanical strength.    Z. Abdollahnejad is with the C-TAC Research Centre, University of Minho, Guimaraes, University of Minho, Portugal  M. Kheradmand is with the C-TAC Research Centre, University of Minho, Guimaraes, University of Minho, Portugal  F.Pacheco Torgal is with the C-TAC Research Centre, University of Minho, Guimaraes, University of Minho, Portugal (phone:351510200; fax 351253510213; email:torgal@civil.uminho.pt) II. EXPERIMENTAL A. Materials and Design The raw materials used for the preparation of the hybrid cement mortars were fly ash (FA), calcium hydroxide (CH), fine aggregate, milled glass (MG) and sodium hydroxide solution. The fly ash was obtained from The PEGO Thermal Power Plant in Portugal and it was classified as class F according to ASTM-C618 standard. The calcium hydroxide used in this study had a commercial name of Lusical H100 and chemical composition of Ca(OH)2 ≥ 93% and MgO ≤ 3. Waste soda lime silicate glass was provided by the use of glass bottles that were ground for one hour in a ball mill. The density of the milled glass was 1.27 g/cm3. Solid sodium hydroxide were obtained from commercially available product of ERCROS, S.A., Spain, were used to prepare three solutions with different concentration (4M and 12M). The chemical composition of the sodium hydroxide was composed of 25%Na2O and 75%H2O. The NaOH mix was made one day prior to use in order to have a homogenous solution at the time of mortar preparation. A sand/binder ratio of 4 was used. The sand was used as inert filler provided from the MIBAL, Minas de Barqueiros, S.A. Portugal. Two commercial supersplasticizers supplied by BASF and SIKA were used. Its content was 0.1% of the binder weight. One is a polycarboxylate-based admixture and the other a lignosulfonate-based. Two activator/binder ratios were used (0.4 and 0.5). Table 1 show the compositions of the 32 mortars. B. Production and Testing In the batching process of the mortars, fly ash, fine aggregate, calcium hydroxide and milled glass were mixed for 2 min. Then, the combination of sodium hydroxide and water reducer agents were added and again mixed for 5 min. The workability of the mortars was assessed by using a truncated conical mould and a jolting table according to the EN 1015-3 [11]. The workability of mix compositions was assessed by using relative slump in percentage, which was computed based on the following equation, 100)1)((0×−=Γddp               (1)   F.Pacheco Torgal is with the C-TAC Research Centre, University of Minho, Guimaraes, University of Minho, Portugal (phone:351510200; fax:351253510213; Z. Abdollahnejad, M. Kheradmand, F.Pacheco Torgal Flow Performance of Hybrid Cement based Mortars   Table I.  MIX COMPOSITIONS (kg/m3) Mix composition FA CH MG NaOH Sand 80FA_10CH_10MG_4M_0.5A/B 377 47 47 236 1884 75FA_10CH_15MG_4M_0.5A/B 350 47 70 233 1864 70FA_10CH_20MG_4M_0.5A/B 328 46 92 230 1844 80FA_10CH_10MG_12M_0.5A/B 377 47 47 236 1884 75FA_10CH_15MG_12M_0.5A/B 350 47 70 233 1864 70FA_10CH_20MG_12M_0.5A/B 328 46 92 230 1844 80FA_10CH_10MG_4M_0.5A/B_0.1% Poly. 377 47 47 236 1884 75FA_10CH_15MG_4M_0.5A/B_0.1% Poly. 350 47 70 233 1864 70FA_10CH_20MG_4M_0.5A/B_0.1% Poly. 328 46 92 230 1844 80FA_10CH_10MG_12M_0.5A/B_0.1% Poly. 377 47 47 236 1884 75FA_10CH_15MG_12M_0.5A/B_0.1% Poly. 350 47 70 233 1864 70FA_10CH_20MG_12M_0.5A/B_0.1% Poly. 328 46 92 230 1844 80FA_10CH_10MG_4M_0.5A/B_0.1% Ligno. 377 47 47 236 1884 75FA_10CH_15MG_4M_0.5A/B_0.1% Ligno. 350 47 70 233 1864 70FA_10CH_20MG_4M_0.5A/B_0.1% Ligno. 328 46 92 230 1844 80FA_10CH_10MG_12M_0.5A/B_0.1% Ligno. 377 47 47 236 1884 75FA_10CH_15MG_12M_0.5A/B_0.1% Ligno. 350 47 70 233 1864 70FA_10CH_20MG_12M_0.5A/B_0.1% Ligno. 328 46 92 230 1844 80FA_10CH_10MG_4M_0.4A/B 385 48 48 193 1928 75FA_10CH_15MG_4M_0.4A/B 358 48 72 191 1908 70FA_10CH_20MG_4M_0.4A/B 330 47 94 189 1888 80FA_10CH_10MG_12M_0.4A/B 385 48 48 193 1928 75FA_10CH_15MG_12M_0.4A/B 358 48 72 191 1908 70FA_10CH_20MG_12M_0.4A/B 330 47 94 189 1888 80FA_10CH_10MG_4M_0.4A/B_0.1% Poly. 385 48 48 193 1928 75FA_10CH_15MG_4M_0.4A/B_0.1% Poly. 358 48 72 191 1908 70FA_10CH_20MG_4M_0.4A/B_0.1% Poly. 330 47 94 189 1888 80FA_10CH_10MG_12M_0.4A/B_0.1% Poly. 385 48 48 193 1928 75FA_10CH_15MG_12M_0.4A/B_0.1% Poly. 358 48 72 191 1908 70FA_10CH_20MG_12M_0.4A/B_0.1% Poly. 330 47 94 189 1888 80FA_10CH_10MG_4M_0.4A/B_0.1% Ligno. 385 48 48 193 1928 75FA_10CH_15MG_4M_0.4A/B_0.1% Ligno. 358 48 72 191 1908 70FA_10CH_20MG_4M_0.4A/B_0.1% Ligno. 330 47 94 189 1888 80FA_10CH_10MG_12M_0.4A/B_0.1% Ligno. 385 48 48 193 1928 75FA_10CH_15MG_12M_0.4A/B_0.1% Ligno. 358 48 72 191 1908 70FA_10CH_20MG_12M_0.4A/B_0.1% Ligno. 330 47 94 189 1888 where, Гp is relative slump, d is the average of two measured ortigonal diameters of the paste spread and d0 is bottom diameter of the conical cone and considered to 100 mm. For compressive testing the mortars were cast into cubic molds (50×50×50 mm3. After 24 hours, specimens were demolded and cured for 28 days at ambient temperature of laboratory with average temperature of 27 0C and 70% HR The cubic specimens were assessed under compressive load with a constant displacement rate of 0.30 N/mm2.s, based on the ASTM C109 recommendation [12]. The compressive load was measured with a load cell of 200 kN capacity. III. RESULTS AND DISCUSSION Fig 1 and 2 shows the compressive strength and flow performance for references mixtures according to sodium hydroxide concentration and water/binder ratio.      Fig 1. Compressive strength versus flow for reference mixtures with three sodium hydroxide concentrations (4 M and 12M) and two water/binder concentrations: A/B=0.4   0204060801001200246810 80FA_10CH_10MG 75FA_10CH_15MG 70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa)Compressive strengthFlowSodium Hydroxide concentration 4M Sodium Hydroxide concentration 12 M     Fig 2. Compressive strength versus flow for reference mixtures with three sodium hydroxide concentrations (4M and 12M) and two water/binder concentrations: A/B=0.5  The results show that references mixtures with an activator/binder (A/B=0.4) show no flow at all being unsuitable for construction purposes. This is independent of the sodium hydroxide concentration and the waste soda lime silicate glass content. When the water/binder ratio increased to 0.5 a minor increase in the flow is noticed. Again it seems that the composition and the sodium hydroxide concentration does not play a relevant role in the flow. The fact that this study used a sand/binder ratio of 4 may help to explain the low flow results. Other authors use a sand/binder ratio of just 2.2 because higher valued greatly reduce the flow [9]. For a A/B=0.5 all mixtures show a compressive strength below 2MPa which have not value for construction purposes. The reduction of the activator binder shows a maximum compressive strength of almost 9 MPa for mixture with 10% replacement of fly ash by waste soda lime silicate glass and a sodium concentration of 8M. The reason may lies on the fact that for low sodium hydroxide concentrations the main hydration product formed is a CSH gel [13].This compressive strength level is enough for renders or masonry units.     Fig 3. Compressive strength versus flow for 0.1% Polycarboxylate mixtures with three sodium hydroxide concentrations (4 M, above 12M) and two water/binder concentrations: A/B=0.4   Mixtures with a sodium concentration of 4M show decreased strength with the replacement of fly ash by waste soda lime silicate glass. However, when the sodium concentration 12 M is used the compressive strength is not influenced by the waste soda lime silicate glass content. The flow and compressive strength for mixtures with 0.1% polycarboxylate admixture are shown in Fig 3 and 4 while the data for mixtures with lignosulphonate are shown in Figs 5 and 6. The results show that the polycarboxylate was not capable to induce flow for mixtures with A/B=0.4. However, the mixtures with a water/binder ratio of 0.5 and 20% waste glass showed almost 40% flow. A flow reduction is noticed for higher sodium hydroxide concentration. These results are not in agreement of other authors [14] who noticed a reduction on workability for polycarboxylates. The lignosulphonate shows a similar behavior. While the lignosulphonate admixture works based on electrostatic repulsion, the polycarboxylate admixture in addition to electrostatic repulsion benefits from steric repulsion produced by lateral ether chains on the molecule of the modified lignosulphonate admixture [15].  0204060801001200246810 80FA_10CH_10MG 75FA_10CH_15MG 70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG 75FA_10CH_15MG 70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlowSodium Hydroxide concentration 4 M Sodium Hydroxide concentration 12 M Sodium Hydroxide concentration 4 M Sodium Hydroxide concentration 12 M     Fig 4. Compressive strength versus flow for 0.1% Polycarboxylate mixtures with three sodium hydroxide concentrations (4 M  and 12M) and two water/binder concentrations: A/B=0.5   As to the mechanical performance mixtures with an activator/binder of 0.5 no strength increase was noticed with the exception of the mixture with 10% replacement of fly ash by waste soda lime silicate glass and a sodium concentration of 4M. As to the ones with the reduced activator/binder ratio some compressive strength decrease are noticed. Other authors suggest that this compressive strength reduction may be due to the fact that those admixtures are not stable on high basic media [16].   IV. CONCLUSIONS The results show that the two commercial mortars show similar ability to slightly increase the flow of mortars with lower sodium hydroxide concentration. Both being more effective than the biopolymer admixture. A mixture based on 80% fly ash, 10% calcium hydroxide and 10% waste soda lime silicate glass showed the highest compressive strength. A compressive strength decrease was noticed concerning the use of the three admixtures that could be due to the fact that those admixtures are not stable in high basic media.      Fig 5. Compressive strength versus flow for 0.1% Lignosulphonate mixtures with three sodium hydroxide concentrations (4 M and 12M) and two water/binder concentrations: A/B=0.4   V.ACKNOWLEDGMENTS The authors would like to acknowledge the financial support of the Foundation for Science and Technology (FCT) in the frame of project IF/00706/2014-UM.2.15        0204060801001200246810 80FA_10CH_10MG 75FA_10CH_15MG 70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG 75FA_10CH_15MG 70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlowSodium Hydroxide concentration 4 M Sodium Hydroxide concentration 12 M Sodium Hydroxide concentration 4 M Sodium Hydroxide concentration 12 M     Fig 6. Compressive strength versus flow for 0.1% Lignosulphonate mixtures with three sodium hydroxide concentrations (4 M and 12M) and two water/binder concentrations: A/B=0.5 REFERENCES   [1] C. Shi, A. Fernandez-Jimenez, A. Palomo, “New cements for the 21st century: The pursuit of an alternative for Portland cement,” Cement and Concrete Research vol.41, pp.750-763, 2011. [2] I. Garcia-Lodeiro, A.Fernandez-Jimenez, A. Palomo, “Variation in hybrid cements over time. Alkaline activation of fly ash-portland cement blends,” Concrete Research 52, 112-122, 2013. [3]  J. Payá, J. Monzó, M. Borrachero, M. Tashima, “Reuse of aluminosilicate industrial waste materials in the production of alkali-activated concrete binders,” in Handbook of Alkali-Activated Cements, Mortars and Concretes, F. Pacheco-Torgal, J. Labrincha, A. Palomo, C. Leonelli, P. Chindaprasirt, Eds, WoodHead Publishing, Cambridge, 2014, pp. 487-518 [4] P. Chindaprasirt, T. Cao, “Reuse of recycled aggregate in the production of alkali-activated concrete. In Handbook of Alkali-Activated Cements, Mortars and Concretes, 519-538, F. Pacheco-Torgal, J. Labrincha, A. Palomo, C. Leonelli, P. Chindaprasirt, Eds, WoodHead Publishing, Cambridge, 2014, pp. 519-538. [5] M. Palácios, F. Puertas, “Effect of superplasticizer and shrinkage-reducing admixtures on alkali-activated slag pastes and mortars. Cem Concr Res vol. 35, pp.1358–67, 2005. [6] P. Chindaprasirt, T. Chareerat, V. Sirivivatnon, “Workability of coarse high calcium fly ash geopolymer,” Cem Concr Compos vol. 29, pp.224–9, 2007. [7] B. Rangan, “Engineering properties of geopolymer concrete”, in Geopolymers, structure, processing, properties and applications, J. Provis, J. Van Deventer Eds, Woodhead Publishing Limited, Abington Hall, Cambridge, 2009. p. 211–226. [8] A. Sathonsaowaphak, P. Chindaprasirt, K. Pimraksa, “Workability and strength of lignite bottom ash geopolymer mortar,” J Hazard Mater vol.168, pp.44–50, 2009. [9] F.Pacheco-Torgal, D.Moura, Y.Ding, S. Jalali, "Composition, strength and workability of alkali-activated metakaolin based mortars", Construction and Building Materials vol. 25, 9: pp.3732 – 3745, 2011. [10] J. Jang, N. Lee, H. Lee, “Fresh and hardened properties of alkali-activated fly ash/slag pastes with superplasticizers,” Construction and Building Materials vol. 50, pp.169–176, 2014. [11] BS EN 1015-3, Methods of test for mortar for masonry. Determination of consistence of fresh mortar (by flow table), UK, 1999. [12] ASTM C109 / C109M-16a, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens), ASTM International, West Conshohocken, 2016. [13] I. Garcia-Lodeiro, S. Donatello, a. Fernandez-Jimenez, A Palomo, “Hydration of hybrid alkaline cement containing a very large proportion of fly ash:A Descriptive Model”, Materials vol. 9, 605;2016. [14] A. Rashad, “A comprehensive overview about the influence of different admixtures and additives on the properties of alkali-activated fly ash,” Materials and Design 53, pp.1005–102, 2014. [15] B. Nematollahi, J. Sanjayan, “Effect of different superplasticizers and activator combinations on workability and strength of fly ash based geopolymer,” Materials and Design vol. 57, pp.667-672, 2014. [16] M. Palacios, F. Puertas, “Stability of superplasticizers and shrinkage reducing admixtures in highly basic media,” Mater de Constr vol. 54(276):pp.65–86, 2004.       020406080100120024681080FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa)Compressive strengthFlow0204060801001200246810 80FA_10CH_10MG75FA_10CH_15MG70FA_10CH_20MGFlow (%)Compressive strength (MPa) Compressive strengthFlowSodium Hydroxide concentration 4 M Sodium Hydroxide concentration 12 M 

Flow performance of hybrid cement based mortars

The workability of hybrid alkaline cements is a field of knowledge that still needs further research efforts. This paper reports experimental results of 32 hybrid cement mixes regarding the joint effect of sodium hydroxide concentration, the use of a commercial superplasticizer and a biopolymer on the flow and compressive strength performance. The results show that the use of commercial admixtures led to a slightly increase in the flow of mortars with lower sodium hydroxide concentration

Flow performance of hybrid cement based mortars

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