Scholarly article on topic 'Performance of Ternary Binder Blend Containing Cement, Waste Gypsum Wall Boards and Blast Furnace Slag in CLSM'

Performance of Ternary Binder Blend Containing Cement, Waste Gypsum Wall Boards and Blast Furnace Slag in CLSM Academic research paper on "Materials engineering"

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{CLSM / "gypsum wall board" / GGBS / "stone dust"}

Abstract of research paper on Materials engineering, author of scientific article — T. Raghavendra, Y.H. Siddanagouda, Fayaz Jawad, C.Y. Adarsha, B.C. Udayashankar

Abstract Controlled low strength materials (CLSM), is a self-flowing cementitious backfill material, most suitable for sustainability objectives since it makes use of wastes in large quantities. Wasted gypsum wall boards (drywalls), a construction & demolition waste, are known to pollute atmosphere by releasing harmful H2S gas when dumped at landfills. Use of waste drywalls with flyash, as cement replacement in concrete and CLSM, have resulted in low strength mixes at initial & later ages, respectively. In this paper powdered drywalls with ground granulated blast furnace slag (GGBS), was used as secondary cementitious material along with stone dust as fine aggregates, to produce sustainable CLSM mixtures with varying binder ratios and water contents. Reduction in compressive strength at later ages was not observed for mixes with low water contents, hence use of GGBS instead of flyash with lesser water contents, is effective in resisting detrimental effects of sulfates present in drywalls.

Academic research paper on topic "Performance of Ternary Binder Blend Containing Cement, Waste Gypsum Wall Boards and Blast Furnace Slag in CLSM"

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Procedía Engineering 145 (2016) 104- 111

Procedía Engineering

www.elsevier.com/locate/procedia

International Conference on Sustainable Design, Engineering and Construction

Performance of ternary binder blend containing cement, waste gypsum wall boards and blast furnace slag in CLSM

T. Raghavendraa*, Y. H. Siddanagoudab, Fayaz Jawada, C.Y. Adarshaa and B.C. Udayashankara

aDepartment of CivilEngineering, R. V. College of Engineering, Visvesvaraya Technological University, Bengaluru 560059, India hDepartment of Civil Engineering, P. V.P. Polytechnic, Bengaluru 560056, India

Abstract

Controlled low strength materials (CLSM), is a self-flowing cementitious backfill material, most suitable for sustainability objectives since it makes use of wastes in large quantities. Wasted gypsum wall boards (drywalls), a construction & demolition waste, are known to pollute atmosphere by releasing harmful H2S gas when dumped at landfills. Use of waste drywalls with flyash, as cement replacement in concrete and CLSM, have resulted in low strength mixes at initial & later ages, respectively. In this paper powdered drywalls with ground granulated blast furnace slag (GGBS), was used as secondary cementitious material along with stone dust as fine aggregates, to produce sustainable CLSM mixtures with varying binder ratios and water contents. Reduction in compressive strength at later ages was not observed for mixes with low water contents, hence use of GGBS instead of flyash with lesser water contents, is effective in resisting detrimental effects of sulfates present in drywalls.

© 2016 The Authors.PublishedbyElsevierLtd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-reviewunderresponsibility of the organizing committee of ICSDEC 2016

Keywords: CLSM; gypsum wall board, GGBS; stone dust

* Corresponding author. Tel.: +91-984-509-3152 E-mail address: raghavendrat@rvce.edu.in

1877-7058 © 2016 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 ICSDEC 2016

doi:10.1016/j.proeng.2016.04.027

1. Introduction

CLSM is defined by ACI Committee-229 [1] as flowable cementitious slurry that results in a compressive strength of 8.3MPa or less. CLSM applications require unconfined compressive strengths in the range of 2.1 MPa or less, so as to allow future excavation of previously laid surfaces for alterations as the need arises. The upper limit of 8.3MPa allows using this material for structural fill under buildings where future excavation is unlikely. CLSM requires no compaction (consolidation) or curing to achieve the desired strength unlike soil cement and offers a direct means to utilize wide spectrum of waste materials which otherwise pose a problem to environment in their safe disposal. CLSM is a combination of fine or coarse aggregates, cement, pozzolanic materials, water and admixtures. Natural sand as fine aggregate is the major component for most of CLSM mixes produced. CLSM benefits are reduced labor requirement compared to compacted earth fill, speedy construction, easy placement in inaccessible zones and the ability to manually re-excavate for relaying utilities if required.

Gypsum wall boards (drywalls) are widely used in various construction activities for many useful reasons. Wasted gypsum wall boards resulting either due to new construction activity or demolition of an existing old building, are usually dumped nearby road side; which eventually get transported to nearby landfills. It is reported that these drywalls release harmful H2S gas to the atmosphere under certain anaerobic and temperature conditions[2-7]. Hence it becomes necessary from public health point of view to re-use these wasted drywalls and avoid their presence in large quantities at landfills. In literature [2] powdered drywalls were used as a binder along with cement and Class C fly ash, to produce concrete. Maximum 10% (by weight) replacement to binder was recommended as higher dosages of these drywalls were detrimental to concrete. This ensured only lesser usage of drywalls, but usage in terms of large quantities was the only solution to reduce harmful effects of these drywalls. In literature [3] powdered gypsum wall boards (PGP) were used as a binder to produce CLSM along with small quantity of cement and large quantities of Class F fly ash. 60.86-51.85% (by weight) replacement to binder was achieved and CLSM mixes from low to high strength's were generated. Though the drywalls were utilized in large quantities their detrimental effects on CLSM were reported that 56 days strength reduced by -7% to -36% when compared with 28 days strength.

Stone quarry wastes are produced while cutting huge quarry rocks to the desired shapes. Stone dust fines are disposed on land and are a major environmental hazard in urban areas and random disposal of stone dust fines may lead to health hazards [8]. Hence it is necessary to re-use this stone dust in large quantities and also reduce the burden on landfills. Many literatures are available on use of stone dust in CLSM [9], concretes [10] and mortars [11]. Ground granulated blast furnace slag (GGBS) is an industrial by-product and its use in concrete industry is recognized by Leadership in Energy and Environmental Design (LEED). Hence use of GGBS in CLSM will add points towards LEED certification and improve the sustainability of the project. GGBS is widely used as secondary cementitious material in CLSM [12,13], pozzolanic cements [14] and concretes [15].

In this paper, experimental studies on new CLSM mixes were performed using the above described wastes both as binders and fillers in large quantities. CLSM mixes were produced for CM 1:1 proportion and named as GG series. A novel ternary binder blend comprising of cement + ground granulated blast furnace slag + powdered gypsum wall boards as binder and stone dust as filler in complete replacement to natural sand was examined. Fresh and hardened properties such as spread flow, Marsh flow and un-confined compressive strength at increasing ages of 3, 7, 28 and 56 days were investigated. To activate the binder blend of GGBS + PGP, few additional mixes were prepared using soda ash as an activator and the results were compared with the mixes prepared without soda ash. 7486.9% (by weight) of total binder content was composed of PGP + GGBS, and 60.86-51.85% (by weight) of total binder content was replaced by PGP. It was found that soda ash as an activator have no appreciable impact on the strength results, and the later age strengths of CLSM mixes with 50-60% (by weight) water contents reduced after 28 days due to use of gypsum wall boards [3]. Reduced compressive strengths was not observed at 56 days age for CLSM mixes of 45% (by weight) water contents only.

Predictive flow and strength phenomenological models [3,12,13] were developed based on wide range of experimental results. These models were compared with independent set of experimental results and found that the predictions are acceptable within accuracy range required for engineering decisions. As described in literatures, the benefit of these predictive models would be saving in time and effort if one has to design the mix for different proportions at any point of time. Preparation of only one trial mix at the reference value is necessary, so that the

required flow and strength values may be arrived at a particular value of water content and binder/water ratio (by weight) or vice-versa.

2. Materials and methods

2.1. Experimental investigation

The waste drywalls in powdered form was used as a binder along with cement (C) and GGBS in varying GGBS/C (Ground granulated blast furnace slag to cement) and PGP/C (Powdered gypsum wall boards to cement) ratios by weight, respectively. Table 1 illustrates the mix proportions of CLSM mixes generated. Stone dust was used as fine aggregates. Water content was varied from 45-60% by weight of total dry mixture, at 5% increments. This resulted in four water contents for each GGBS/C or PGP/C ratio. A total of 20 CLSM mixes were generated with five mixes ID (GG1 to GG5). For each mix ID and a particular water content minimum 20 cylindrical specimens were cast. A total of 400 (and more) specimens were cast and tested for GG series. Acrylic moulds of diameter 40mm and height 80mm were used. The fresh CLSM mix was were allowed to harden for 1 day and then, the specimens were de-moulded and stored in room temperature and allowed for air-curing.

Table 1. Mix proportions of CLSM mixes

Mix ID GGBS/C ratio PGP/C ratio Cement (C), g/100g Ground granulated blast furnace slag (GGBS), g/100g Powdered Gypsum Wall board (PGP), g/100g Quarry dust, g/100g

GG1 2.00 4.67 6.52 13.05 30.43 50

GG2 1.50 3.50 8.33 12.51 29.16 50

GG3 1.20 2.80 10.00 12.00 28.00 50

GG4 1.00 2.33 11.54 11.54 26.92 50

GG5 0.86 2.00 12.96 11.11 25.93 50

Note: Water content is varied as 45%, 50%, 55% & 60%, to produce mixes with RFA in the range 5-15.

2.2. Materials

The materials adopted in this research are the same which are described in the literature [3], except for GGBS. Ordinary Portland cement (C) of 53 grade was used and its physical properties were determined according to IS: 12269 [16] specifications. Initial and final setting times of cement were found to be 43 min and 218 min, respectively with a specific gravity of 3.09. Ground granulated blast furnace slag (GGBS) was used as secondary cementitious material and was procured from JSW Steel Ltd., at Toranagallu, Bellary-Hospet, Karnataka, India; having a specific gravity of 2.82. Waste gypsum wall board sheets were used as secondary cementitious material which were sourced from new construction sites and demolition sites in Bangalore, and was crushed manually. Powdered gypsum wall board passing through 4.75mm sieve size was used with a specific gravity of 1.76. The specific surface area determined by Blaine's permeability method for cement, GGBS, powdered gypsum wall board and stone dust were 307m2/kg, 327m2/kg, 169m2/kg and 381m2/kg, respectively. Stone dust having a specific gravity of 2.46 was sourced from stone quarry waste dump site at Bidadi, Bangalore, Karnataka, India. Table 2 gives the elemental compositions of cement, powdered gypsum wall board, GGBS and quarry dust, obtained from the Scanning Electron Microscopy (SEM)-Energy Dispersive X-ray Spectroscopy (EDS). The particle size distribution of materials is illustrated in Fig. 1.

2.3. Engineering properties

The spread flow test [3] was conducted using an open ended cylinder of 75mm diameter and 150mm height, according to ASTM D 6103 [17]. The flow diameter (D) measured in six directions was averaged and relative flow

area (RFA) was calculated using the formula (D/75) -1. Marsh flow test [3] was conducted using a brass cone of 10mm smooth aperture diameter, according to ASTM C939 [18]. The Marsh flow time was averaged out of three trials. Un-confined compression strength tests [3] were carried out at 3, 7, 28 and 56 days age, respectively; using a modified CBR apparatus. The results from minimum of five specimens were recorded and averaged.

Fig. 1. Particle size distribution of materials.

Table 2. Elemental composition of materials, obtained from SEM - EDS analysis. Spectrum processing : No peaks omitted

Processing option : All elements analyzed (Normalised)

Number of iterations = 4

Standard :

C CaC03 l-Jun-1999 12:00 AM O Si02 l-Jun-1999 12:00 AM Mg MgO l-Jun-1999 12:00 AM Na Albite l-Jun-1999 12:00 AM Al A1203 l-Jun-1999 12:00 AM

Si Si02 l-Jun-1999 12:00 AM S FeS2 l-Jun-1999 12:00 AM K MAD-10 Feldspar l-Jun-1999 12:00 AM Ca Wollastonite l-Jun-1999 12:00 AM Fe Fe l-Jun-1999 12:00 AM

Element Cement Powdered board gypsum wall GGBS Quarry dust

Weight % Atomic % Weight % Atomic % Weight % Atomic % Weight % Atomic %

CK 5.40 9.62 4.42 7.99

OK 46.49 62.21 51.54 70.69 40.91 55.55 55.39 68.72

MgK 4.06 3.63

NaK 2.35 2.03

A1K 2.61 2.07 0.00 0.00 8.17 6.58 5.54 4.08

SiK 7.64 5.82 0.44 0.34 14.00 10.83 32.82 23.19

SK 2.15 1.44 19.52 13.36

KK 0.93 0.51 3.19 1.62

CaK 33.08 17.67 28.49 15.60 28.44 15.42 0.72 0.35

Fe K 1.70 0.65

Totals 100 100 100 100

2.4. Predictive flow and strength models

Phenomenological models as described in literatures [3,12,13] were developed using the flow and strength results of GG1, GG2, GG3 and GG5 CLSM mixes only. In the development of flow model all flow values were normalized with respect to a reference flow value at w=55% (by weight). The normalized values were plotted and illustrated in Fig. 2 (a); the trend line equation represents the flow model in terms of RFA. In the development of strength model all strength values at respective ages, were normalized with respect to a reference strength value at B/w=1.0 (binder to water ratio). The normalized values were plotted and illustrated in Fig. 2 (b); the trend line equations represent the strength model in terms of B/w ratio.

Fig. 2. (a) Generalized flow model; (b) Generalized strength models

The generalized flow model for GG series is "{RFA/(RFA@w=55%)} = 0.066w-2.6". The generalized strength models for GG series at 3, 7, 28 and 56 days are "{S/(S@B/w=1.0)} = 1.93(B/w) - 0.926"; "{S/(S@B/w = 1.0)} = 1.338(B/w)-0.357"; "{S/(S@B/w=1.0)} = 1.806(B/w)-0.839"; "{S/(S@B/w=1.0)} = 2.569(B/w)-1.481"; respectively.

2.5. Validation of predictive models

The experimental results of GG4 series were compared with the predicted values from flow and strength phenomenological models. Fig. 3 illustrates the validation of the predicted models with respect to experimental results. The predicted flow value was calculated using the flow of GG4 mix at the reference value (w=55%) of the model. This flow value in terms of RFA was substituted in denominator of LHS of the generalized flow equation, and RFA at required water contents were calculated. Similar approach was adopted to predict strength values. It is observed that the predicted values are within the range required for engineering decisions. Hence the usual multiple trial and error process to proportion CLSM mix, if required in future using same ingredients in 1:1 proportion, can be reduced to a single trial. The results and models are generated using these waste materials from a particular source in CM 1:1 proportion. If the proportions are changed, the slope of the trend line and hence the predicted values may be different since the water demand and subsequent strength development of CLSM mixes will vary.

3. Results and discussions

The un-confined compressive strength results are illustrated in Fig. 4 and 5. It was observed that the strength increased at increasing ages of 3, 7 and 28 days for all the 20 CLSM mixes. The strength values reduced after 28

days i.e. at the age of 56 days, for CLSM mixes of higher water contents of 50%, 55& and 60%. This reduced compressive strength values is due to the presence of sulfates in drywalls used (refer Table 2) and their detrimental effects on hardened CLSM specimens leading to expansive cracks. Similar behavior was observed in the literature [3] for CLSM mixes produced using the binder blend of cement + Class F fly ash + powdered gypsum wall board. Decrease in strength values were not observed for 5 CLSM mixes having the lowest water content of 45%. Hence it may be noted that binder blend of cement + GGBS + drywalls and lesser water contents, are effective in resisting the detrimental effects of sulfates present in drywalls. About 30-48%, 67-95%, 93-100% of maximum strength gained was observed at 3, 7 and 28 days, respectively. About 0.5-25% reduction in strength with respect to 28 day age strength was observed at 56 day age.

Fig. 3. (a) Validation of phenomenological model for flow; (b) Validation of phenomenological model for strength

® £ 3

■ GG1

GG3 ■ GG-)

b 4.50

|j 2.00 .3 l.so

0.50 0.00

7 28 56 3 7 28

Age 11. Days Age id Days

Fig. 4. (a) Strength variations at w=45%; (b) Strength variations at w=50%

■ GG1

■ CtG2

GG3 ■ GG4

Fig. 5. (a) Strength variations at w=55%; (b) Strength variations at w=60%

Compared to literature [3], GG series mixes have high early age strength development and lesser percentages of strength reduction at 56 days age, due to the presence of sulfates in gypsum wall board. Table 3 gives the average strength results for GG1-A and GG2-A series CLSM mixes with soda ash as an activator. Marginal increase in strength values of CLSM mixes with soda ash may not be necessary for usual applications of CLSM.

The average flow results are given in Fig. 6. Flow values in terms of RFA for GG series mixes varied from 3.8417.20. Most of the mixes have RFA in the range 5-15 [12], required for self flowing and leveling consistency. Increase in water demand was observed for mixes with higher dosages of drywalls, GGBS and stone dust. This is due to high surface area and fine particle sizes of all the ingredients involved. Marsh flow time varied from 44 to 72 seconds for water content of 60% (by weight of total mixture weight) in all mixes, and zero Marsh flow time was recorded for remaining water contents. Similar behavior of CLSM mixes was observed in Marsh flow time of CLSM mixes containing binder blend of cement + Class F fly ash + powdered gypsum wall board [3]. Compared to literature [3], GG series mixes have reduced Marsh flow time for higher dosages of drywalls, GGBS and stone dust.

45 50 55 60

Water Content (w%)

Fig. 6. Flow variations of CLSM mixes

Table 3. Average strength results for GG1 and GG2 series CLSM mixes, with soda ash as an activator.

Mix w, B/w Experiment values

ID % ratio Average Compressive Strength, MPa

3 Day 7 Day 28 Day 56 Day

GG1-A 45 1.1 1.96 4.39 5.31 5.8

GGBS/C=2; 50 1.0 1.73 3.44 4.44 4.49

PGP/C=4.67 55 0.9 1.2 2.55 3.84 3.29

60 0.8 1.05 1.37 1.75 1.23

GG2-A 45 1.1 1.86 3.82 4.23 2.71

GGBS/C=1.5; 50 1.0 1.61 3.11 3.24 2.45

PGP/C=3.5 55 0.9 1.43 2.66 3.04 2.88

60 0.8 1.72 2.25 2.92 2.55

4. Conclusions

The following conclusions are drawn on the basis of the results presented in this paper:

• CLSM mixes comprising ternary binder blend of cement + ground granulated blast furnace slag + powdered gypsum wall board, reported reduced compressive strength values after 28 days age. The reduction in strength was not observed for mixes with water content of 45%. About -0.5 to -0.25% of strength reduction was observed for mixes with water contents of 50%, 55% and 60%, respectively.

• Use of GGBS instead of Class F fly ash along with cement and stone dust, is recommended for production of CLSM mixes with lesser water contents to effectively overcome the detrimental effects of sulfates present in drywalls. The lesser water content required may be determined based on the self flow and consolidation criteria of a particular application.

• Wasted drywalls use in CLSM will reduce pollution of atmosphere due to release of H2S gas at landfills.

• Water demand of CLSM mixes increased due to use of drywalls, GGBS and stone dust, in large quantities.

• The spread flow and Marsh flow time for GGBS based CLSM mixes reduced when compared to Class F fly ash based mixes and Marsh flow time was recorded only for mixes of 60% water contents as other water contents resulted in zero flow.

• Utilization of GGBS, drywalls and stone dust, which are by-products and waste materials, will reduce the burden on landfills and hence add to sustainability of the concrete industry.

Acknowledgements

This research (or a portion of) was performed using facilities at CeNSE, funded by Department of Information Technology, Govt, of India and located at Indian Institute of Science, Bangalore; and Civil-Aid Technoclinic Pvt. Ltd. (A Bureau Veritas Group Company), Bangalore.

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