Performance and Compatibility of Phosphonate-Based Superplasticizers for Concrete

buildings

Article Performance and Compatibility of Phosphonate-Based Superplasticizers for Concrete

Luigi Coppola 1, Sergio Lorenzi 1 , Patricia Kara 2,* and Stefano Garlati 3

1 Department of Engineering and Applied Sciences (DISA), Department of Engineering and Applied Sciences, University of Bergamo, 24044 Dalmine, Italy; [email protected] (L.C.), [email protected] (S.L.) 2 Energy & Materials in Infrastructure & Buildings (EMIB), Faculty of Applied Engineering, University of Antwerp, 2020 Antwerp, Belgium 3 Giovanni Bozzetto S.p.A., 24040 Filago (BG), Italy; [email protected] * Correspondence: [email protected]; Tel.: +32-3-265-8851

Received: 15 May 2017; Accepted: 4 July 2017; Published: 7 July 2017

Abstract: The paper deals with the effectiveness of an innovative phosphonate-based superplasticizer (PNH) for ready mixed concrete. Concrete specimens were manufactured by considering a constant initial workability, equal to 220 mm slump at the end of the mixing procedure. Workability was measured at 0, 30, and 60 min to evaluate the workability retention performances of the innovative superplasticizer. Compressive tests at 1, 7, and 28 days were carried out to evaluate the influence of the phosphonate-based superplasticizer on concrete setting and hardening. The concrete mixes were designed by considering 13 different cements to assess the superplasticizer-cement compatibility. The PNH-based admixture showed a better performance in terms of water reduction and workability retention with respect to napthalenesulphonate based admixtures (NSF); however, a higher dosage of PNH with respect to polycarboxylate ethers (PCEs) was needed to get the same initial ﬂuidity.

Keywords: concrete; phosphonate-based admixtures; compatibility; workability

1. Introduction Since the last decade of the 20th century, advances in cement-based materials are mainly sustained by research activities focused on raw materials consumption, optimization of mixes, and the reuse of by-products to improve performances in a logic of sustainable development in the building industry [1–6]. All the studies in this field are characterized by the need to use admixtures tailored to improve concrete performance—both mechanical and rheological—in mixes characterized by high specificity due to the presence of a variable amount and nature of recycled raw materials. In such outlooks, superplasticizers can be considered ‘green additions’ because they permit the manufacture of sustainable and durable structures, further reducing the need of repair/rebuild and quarry raw materials. During the last 40 years, concrete technology has made considerable progress due to development and the use of very efficient admixtures designed in order to improve physical, rheological, mechanical properties of concrete and its durability [7]. Naphthalenesulphonate-based admixtures (NSF) have been used as chemical admixtures since approximately 1930. Since 2000, the development of an innovative class of superplasticizers—such as polycarboxylate ether-based plasticizers (PCE)—caused a big change in the field of concrete technology. PCEs significantly improved the performance of concrete in terms of workability retention up to a couple of hours, while also providing 2–3 times more effectiveness in terms of water reduction, cohesion, and rate of strength development than NSFs [8]. In addition, considering a relatively linear relationship over a significant admixture dosage range, it has allowed these chemicals to be used in a cost effective way to meet the requirements of concrete mix design.

Buildings 2017, 7, 62; doi:10.3390/buildings7030062 www.mdpi.com/journal/buildings Buildings 2017, 7, 62 2 of 10

The different performances of NSFs and PCEs can be related to the different dispersion mechanism, which is driven almost entirely by electrostatic repulsion in the case of NSF, and significantly by steric hindrance in the case of PCEs [9–13]. Moreover, the possibility of changing several synthesis parameters of the PCEs (molecular weight, backbone length and flexibility, side-chain length, charge density) has led to the development of products characterized by tailored properties for specific applications. The higher efficiency of PCEs leads to a worsening of the well-known compatibility issues between superplasticizer and cement type [14–20]. It has also been reported that the performance variability of PCEs is dependent upon the cement production batch [8]. The incompatibility of the cement-superplasticizer system can lead to unexpected variability of the superplasticizer dosage needed to attain a sufficient workability, poor workability retention, and a compressive strength decrease at an early age. Phosphonic acids and their salts (phosphonates) are known to form complexes with inorganic species influencing the hydration reactions. Phosphonates appear to be much more efficient retarders than many other retarders normally used in concrete practice, for example, to retard the setting time of concrete in hot weather or in the case of long transportation times. The lower pH of aqueous acids improves their chelating or complexing ability, resulting in hindered growth and stabilization of the calcium silicate hydrate on the hydrating C3S phase [21–23]. They have been used in cements, primarily soil/cement mixtures to improve the freeze–thaw properties and salt-resistance [24], in high temperature oil and gas plugging operations, gypsum plasters and as set time extenders for cements. Phosphonates may be classified as superretarders because of their efficiencies [23] and may find applications in controlling slump in superplasticized concrete, mainly in very hot climates or in cases of prolonged transport times. Ramachandran et al. [21] tested different phosphonates and found that diethylenetriamine-penta (methylenephosphonic acid), DTPMP, was the most efficient retarder in OPC pastes. He managed to increase the induction period of an OPC paste from 3 h (reference mix) to more than 72 h using only 0.09 % DTPMP by weight of cement. Gu et al. [25] reported that phosphonates produce a prolonged induction period and a delay of cement hydration ranging from 12 to 42 h at very low dosages (0.03–0.05%). The retarding effect of these admixtures promotes a delay in the setting time and improves the workability retention through a decrease of C3S dissolution rate. Using electrical conductivity and AC impedance methods to investigate early hydration and setting behavior of OPC pastes containing phosphonates, [25] confirmed that phosphonates have strong chelating and complexing capability, and that this effect might hinder calcium hydroxide (CH) and calcium silicate hydrate (CSH) nucleation. Most work related to phosphonate application is to be found only in patents and in the literature from the 1990s, their role in the hydration of Portland cement is not much studied lately. Considering that phosphonates have a super-retarding effect far more efficient than that of other products, their application nowadays in concrete could be a challenge for the future investigation. This present research focuses on the evaluation of the rheological and mechanical behavior of concrete manufactured by means of a new generation of phosphonate-based superplasticizer to improve the cement/admixture compatibility. This research is devoted to the study of an innovative superplasticizer for concrete with higher efficiency in terms of water reduction with respect to polycarboxilate-based admixtures and characterized by a higher compatibility upon different cement types/production batches than NSF-based admixtures.

2. Materials and Methods Concrete mixes manufactured by using 13 different cement types produced by different cement plants were used to evaluate the compatibility of the phosphonate-based superplasticizer (mixed polymer made of poly amine and polyoxyethylene oxide where amminic chain constitutes the backbone and ethylen oxide constitute lateral chains) with respect to commercial naphthalene-based and polycarboxilate-based products. Buildings 2017, 7, 62 3 of 10

The cements were speciﬁcally selected in order to cover the whole Italian production [26]. Chemical compositions of the cements are shown in Table1. Different batches of cements from several cement plants were used. Tests on concrete were carried out using the following cements: • CEM II/A-LL 42.5 R (Limestone Portland Cement) • CEM II/A-LL 32.5 R (Limestone Portland Cement) • CEM II/B-LL 32.5 R (Limestone Portland Cement) • CEM II/B-S 32.5 R (Slag Portland Cement) • CEM III/A 32.5 N (Blast-Furnace Slag Cement) • CEM IV/A (P) 42.5 R (Natural Pozzolanic Cement) • CEM IV/A (V) 42.5 R (Fly Ash Pozzolanic Cement) • CEM IV/A (V) 32.5 R (Natural Pozzolanic Cement)

Table 1. Chemical composition (% by mass) of the cements.

Prod. LOI Cement SiO Al O Fe O TiO CaO MgO SO Na OK O Cl Batch (500 ◦C) 2 2 3 2 3 2 3 2 2 Lot 2 0.92 17.35 3.79 1.65 0.25 59.76 2.77 2.85 0.13 0.69 0.034 CEM II/B-LL 32.5 R Lot 4 0.96 16.59 3.89 1.73 0.12 60.01 2.42 2.67 0.13 0.62 0.020 Lot 2 1.18 26.65 8.49 3.23 0.29 50.27 2.53 2.5 0.30 0.97 0.030 CEM IV/A-V 32.5 R Lot 4 1.42 26.57 7.66 2.86 0.32 50.73 2.05 2.89 0.25 0.94 0.049 Lot 2 0.99 19.96 4.21 2.06 0.20 61.61 2.73 2.85 0.12 0.80 0.040 CEM II/A-LL 42.5 R Lot 4 1.06 18.59 4.11 1.79 0.19 61.41 2.34 3.62 0.10 0.68 0.040 CEM IV/A-P 42.5 R Lot 1 2.52 27.64 8.38 3.83 0.41 49.02 2.04 2.87 0.41 2.02 0.010 CEM III/A 32.5 N Lot 1 1.77 24.58 5.72 2.76 0.30 57.16 3.74 3.10 0.05 0.70 0.020 CEM II/B-S 32.5 R Lot 1 3.07 22.16 5.64 2.54 0.28 56.40 3.78 4.19 0.45 0.85 0.060 CEM II/A-LL 42.5 R Lot 1 6.27 18.74 4.98 2.22 0.28 59.43 3.40 3.28 0.45 0.90 0.050 CEM II/A-LL 42.5 R Lot 3 1.09 18.90 4.63 2.78 0.24 57.02 3.52 3.24 0.25 0.78 0.074 CEM IV/A-V 32.5 R Lot 3 0.60 25.28 7.56 4.43 0.36 52.95 1.94 3.62 0.39 1.12 0.078 CEM II/A-LL 32.5 R Lot 3 1.59 18.53 4.54 2.65 0.25 57.33 3.35 3.17 0.28 0.72 0.024

The performances of the new phosphonate-based superplasticizer (PNH1) were compared to commercial NSF (NSF3) and PCE-based (ACR1) products selected among those most widely used in Italy. The commercial products were tested in previous work [8,19,20]. The main properties of the NSF and PCE-based superplasticizers are summarized in Table2. Concretes with w/c ratio equal to 0.52 and with a cement content of 325 kg/m3 were manufactured. The concrete mix composition is shown in Table3. Particle size distribution of aggregates is shown in Figure1. The superplasticizer dosage was adjusted to attain a constant slump with a value equal to 220–230 mm (UNI EN 12350-2) at the end of the mixing procedure. Workability was measured according to UNI EN 12350-2 and UNI EN 12350-5 at 0, 30 and 60 min. Air entrapping tendency and density were also evaluated on fresh concrete according to UNI EN 12350-6 and UNI EN 12350-7, respectively. The mixing procedure and all the measurements on fresh concrete were carried out at a room temperature of +20 ◦C and a relative humidity equal to 65%. Compressive strength was measured at 1, 7, and 28 days.

Table 2. Main properties of naphthalene, polycarboxylate-and the experimental phoshonate-based superplasticizers.

Properties NSF3 ACR1 PNH1 Molecular weight (MW) (g/mol) 14,000 35,000 3000 MW/Mn 10 2.7 1.2 Side chain length (g/mol) 3000–5000 1000 Monomer type Ester of acrylic or methacrylic acid Amino-methane phosphonic polymer Ionic groups/non-ionic side chains 5 3 Buildings 2017, 7, 62 4 of 10 Buildings 2017, 7, 62 4 of 10

Table 3. Concrete mix composition. Buildings 2017, 7, 62 Table 3. Concrete mix composition. 4 of 10

3 MaterialsMaterials TableGrading Grading 3. Concrete Size Size Distribution Distribution mix composition.(mm) (mm) DosageDosage(kg/m³) (kg/m ) Aggregates 10–20 600 AggregatesMaterials Grading Size Distribution 10–20(mm) Dosage (kg/m³) 600 6–106–10 280 280 Aggregates 10–20 600 3–43–4 295 295 6–10 280 1.50–2.501.50–2.50 295 295 3–4 295 0.6–0.80.6–0.8 110 110 1.50–2.50 295 0.2–0.350.2–0.35 255 255 0.6–0.8 110 FillerFiller 0.08–0.2 0.08–0.2 35 35 0.2–0.35 255 CementCement 325 325 Filler 0.08–0.2 35 WaterWater 169 169 Cement 325 Water 169

FigureFigure 1. 1.Particle Particle size size distribution. distribution. Figure 1. Particle size distribution. 3. Results and Discussions 3.3. Results Results andand DiscussionDiscussions

3.1.3.1.3.1. The The Correlation Correlation between between the the Superplasticizer Superplasticizer Superplasticizer Dosage Dosage Dosage and and and Workability Workability Workability FigureFigure2 2 2shows showsshows the the the meanmean mean value value of of of the the the superplasticizer superplasticizer superplasticizer dosage dosage dosage (the (the (the percentage percentage percentage of dry of of dry polymerdry polymer polymer vs. vs. vs. thethethe cement cement mass) mass)mass) to toto attain attain the the 220–230 220–230 220–230 mm mm mm slump slump slump at at atthe the the end end end of of theof the the mixing mixing mixing procedure. procedure. procedure.

(a) (b) (a) (b) Figure 2. Mean value (a) and RSD (b) of the superplasticizer dosage (% of dry polymer vs. cement Figure 2. Mean value (a) and RSD (b) of the superplasticizer dosage (% of dry polymer vs. cement mass)Figure to 2. attain Mean 220–230 value ( mma) and slump RSD on (b concrete.) of the superplasticizer dosage (% of dry polymer vs. cement mass) to attain 220–230 mm slump on concrete. mass) to attain 220–230 mm slump on concrete. TheThe dosage dosage usedused for the naphthalene naphthalene-based‐based superplasticizer superplasticizer is higher is higher than than for forACR1, ACR1, therefore therefore conﬁrmingconfirmingThe dosage thatthat NSF3NSF3 used superplasticizer for the naphthalene has has lower‐ lowerbased efficiency efﬁciencysuperplasticizer than than ACR1 ACR1 is higherin terms in terms than of water offor water ACR1, reduction. reduction. therefore TheconfirmingThe PNH1 PNH1 admixture admixture that NSF3 showed superplasticizer an an intermediate intermediate has lower dosage dosage efficiency between between than the the two ACR1 two different differentin terms admixture admixtureof water product reduction. product Thefamilies PNH1 (NSF admixture and PCE). showed The RSD an (Relative intermediate Standard dosage Deviation) between values the twoare sensiblydifferent lower admixture in the case product families (NSF and PCE). The RSD (Relative Standard Deviation) values are sensibly lower in the case Buildings 2017, 7, 62 5 of 10

Buildings 2017, 7, 62 5 of 10 families (NSF and PCE). The RSD (Relative Standard Deviation) values are sensibly lower in the case ofof PNH1,PNH1, evidencing evidencing higher higher cement/superplasticizer cement/superplasticizer compatibility compatibility compared compared to both to NSF3both andNSF3 ACR1 and superplasticizers.ACR1 superplasticizers. ACR1 ACR1 confirmed confirmed the highest the highest dosage dosage variability variability and, consequently, and, consequently, the highest the dependencehighest dependence upon cement upon cement type/strength type/strength class. class. NSF3 NSF3 showed, showed, by by contrast, contrast, a a low low performanceperformance variability,variability, as as expected. expected. AlthoughAlthough thethe origin origin of of the the performance performance variability variability observed observed with differentwith different cements cements is not entirely is not understood,entirely understood, it must be it considered must be considered that the adsorption that the ofadsorption the superplasticizers of the superplasticizers onto the cement onto grains the iscement driven grains by both is enthalpicdriven by and both entropic enthalpic contributions and entropic [27 contributions]. In particular, [27]. for PCEIn particular, superplasticizers for PCE atsuperplasticizers surface loadings at closesurface to loadings the monolayer close to adsorption, the monolayer the adsorption, enthalpic contribution the enthalpic decreases contribution and approachesdecreases and zero, approaches while the zero, entropic while contributionthe entropic contribution increases. Inincreases. such conditions, In such conditions, it may happen it may thathappen minor that variations minor variations in cement in cement chemistry chemistry or sulfate or sulfate solubility, solubility, resulting resulting in modifications in modifications of the of solutionthe solution ionic ionic concentration, concentration, affecting affecting the performance the performance of PCE of superplasticizers.PCE superplasticizers. On the On other the hand,other phosphonate-basedhand, phosphonate admixtures‐based admixtures are known are toknown have ato higher have adsorptiona higher adsorption energy and energy are thus and less are prone thus toless variations prone to invariations the solution in the chemistry. solution chemistry. FigureFigure3 shows3 shows the the superplasticizer superplasticizer dosage dosage and the and workability the workability at 60 min. at ACR1 60 min. based ACR1 admixtures based areadmixtures represented are inrepresented the upper-left in zonethe upper of the‐left graph, zone meaning of the thatgraph, they meaning have higher that efficiencythey have in higher terms ofefficiency water reduction in terms and of water workability reduction retention. and workability On the contrary, retention. NSF3 On is in the the contrary, lower-right NSF3 zone is duein the to lowerlower‐ effectivenessright zone due in termsto lower of water effectiveness reduction in and terms poor of workability water reduction retention and compared poor workability to ACR1. PNH1retention is in compared the middle-high to ACR1. zone PNH1 of the is graph,in the middle because‐high they zone have of intermediate the graph, efficiencybecause they between have NSF3intermediate and ACR1, efficiency but outstanding between NSF3 workability and ACR1, retention but outstanding at 60 min. workability Looking through retention each at class60 min. of superplasticizer,Looking through dosageeach class does of superplasticizer, not significantly dosage affect fluidity does not at significantly 60 min. This affect trend fluidity is particularly at 60 min. evidentThis trend in theis particularly case of ACR1 evident and PNH1.in the case NSF3 of ACR1 presented and aPNH1. high variabilityNSF3 presented upon a different high variability cement type/strengthupon different class.cement PNH1 type/strength superplasticizer class. PNH1 showed superplasticizer poor workability showed at 60 poor min workability only for one at cement 60 min (75only mm for slump)one cement and (75 the mm performance slump) and variability the performance is substantially variability in the is substantially 125–180 mm in slump the 125–180 range. ACR1mm slump presented range. under-performances ACR1 presented under on three‐performances different cements on three and different the range cements is almost and similar the range to the is experimentalalmost similar admixture. to the experimental admixture.

250 225 NSF3 200 PNH1 175 ACR1 150 125 100 75 Slump at 60' (mm) Slump at 50 25 0 0 0.1 0.2 0.3 0.4 0.5 0.6 SP dosage (% dry vs cement)

Figure 3.3. Slump value after 60 min asas aa functionfunction ofof thethe superplasticizersuperplasticizer dosage.dosage.

3.2.3.2. Workability FigureFigure4 shows4 shows the meanthe mean value ofvalue slump of after slump 60 min. afterWorkability 60 min. isWorkability lower for NSF is superplasticizedlower for NSF concretesuperplasticized with respect concrete to mixes with manufactured respect to mixes with manufactured PCE products, with as expected.PCE products, as expected. Buildings 2017, 7, 62 6 of 10 BuildingsBuildings 20172017,, 77,, 6262 66 ofof 1010

((aa)) ((bb))

FigureFigureFigure 4.4. 4. SlumpSlumpSlump meanmean mean valuevalue value (( (aaa))) andand and RSDRSD RSD (( (bbb))) afterafter after 6060 60 min min sincesince since mixing mixing procedure. procedure.

PCEPCE productsproducts presentpresent aa higherhigher workabilityworkability retentionretention thanthan NSFNSF‐‐basedbased products,products, confirmingconfirming thatthat PCE products present a higher workability retention than NSF-based products, confirming that the thethe stericsteric hindrancehindrance isis farfar moremore effectiveeffective thanthan thethe electrostaticelectrostatic repulsionrepulsion mechanismmechanism toto grantgrant aa steric hindrance is far more effective than the electrostatic repulsion mechanism to grant a prolonged prolongedprolonged fluidity.fluidity. PNH1PNH1 superplasticizersuperplasticizer showedshowed thethe highesthighest meanmean valuevalue ofof thethe workabilityworkability fluidity. PNH1 superplasticizer showed the highest mean value of the workability retention at 60 min. retentionretention atat 6060 min.min. ThisThis factfact couldcould bebe ascribedascribed toto thethe setset retardationretardation effecteffect ofof thethe phosphonatephosphonate‐‐basedbased This fact could be ascribed to the set retardation effect of the phosphonate-based admixture. The lowest admixture.admixture. TheThe lowestlowest RSDRSD valuevalue inin termsterms ofof slumpslump retentionretention cancan bebe observed;observed; PNH1PNH1 superplasticizersuperplasticizer RSD value in terms of slump retention can be observed; PNH1 superplasticizer also displayed a more alsoalso displayeddisplayed aa moremore reproduciblereproducible valuevalue despitedespite thethe differentdifferent cementcement types/strengthtypes/strength classes.classes. reproducible value despite the different cement types/strength classes. 3.3. Air Content and Density 3.3. Air Air Content Content and Density All tested products showed low air entrapping tendency (see Figure 5), the values are below 1.5% All tested tested products products showed showed low low air air entrapping entrapping tendency tendency (see (see Figure Figure 5),5 the), the values values are are below below 1.5% for all products. PNH1 admixture showed a higher air content than the commercial products. This for1.5% all for products. all products. PNH1 PNH1 admixture admixture showed showed a higher a higher air content air content than the than commercial the commercial products. products. This could be ascribed to the fact that a general purpose defoaming agent was adopted and it was not couldThis could be ascribed be ascribed to the to thefact fact that that a general a general purpose purpose defoaming defoaming agent agent was was adopted adopted and and it it was was not optimized for this specific experimental admixture. Nevertheless, it should be noticed that the values optimized for this specific specific experimental admixture. Nevertheless, it should be noticed that the values are typical for concrete and no anomalous air entrapping tendency of the experimental admixture are typical for concrete and no anomalous air entrapping tendency of the experimental admixture was detected. was detected.

2.0%2.0%

1.5%1.5%

1.0%1.0% Entrapped air air Entrapped Entrapped air air Entrapped 0.5%0.5%

0.0%0.0% NSF3NSF3 PNH1 PNH1 ACR1 ACR1

FigureFigureFigure 5.5. MeanMeanMean valuevalue value ofof of entrappedentrapped entrapped air.air. air.

TheThe density density measurementsmeasurements conducted conductedconducted on onon fresh freshfresh and andand hardened hardenedhardened concrete concreteconcrete (see (see(see Figure FigureFigure6) confirmed 6)6) confirmedconfirmed the thetheentrapped entrappedentrapped air data. airair Thedata.data. density TheThe density valuesdensity are valuesvalues substantially areare substantiallysubstantially similar for all similarsimilar admixtures. forfor allallPNH1 admixtures.admixtures. superplasticizer PNH1PNH1 superplasticizersuperplasticizergenerally showed generallygenerally the lowest showedshowed density valuethethe lowestlowest on fresh densitydensity and hardened valuevalue concreteonon freshfresh compared andand hardenedhardened to the commercial concreteconcrete comparedcomparedproducts. Thetoto thethe commercial commercialcommercial products products.products. generally TheThe commercialcommercial showed higher productsproducts density generallygenerally values showedshowed on hardened higherhigher concrete densitydensity valuesvalueswith respect onon hardenedhardened to fresh concreteconcrete concrete. withwith respectrespect toto freshfresh concrete.concrete. Buildings 2017, 7, 62 7 of 10 Buildings 2017, 7, 62 7 of 10 Buildings 2017, 7, 62 7 of 10 2450 2450 Fresh Hard Fresh Hard 2400 2400 ) 3 ) 3 2350 2350

2300 2300 Density (kg/m

Density (kg/m 2250 2250

2200 2200 NSF3 PNH1 ACR1 NSF3 PNH1 ACR1

FigureFigure 6.6. Density of freshfresh andand hardhard concreteconcrete (mean(mean valuevalue forfor allall cements).cements). Figure 6. Density of fresh and hard concrete (mean value for all cements). 3.4.3.4. CompressiveCompressive StrengthStrength 3.4. Compressive Strength FigureFigure7 shows7 shows the normalizedthe normalized compressive compressive strength strength values (Rc*)values of the(Rc*) three of different the three admixtures. different Figure 7 shows the normalized compressive strength values (Rc*) of the three different Rc*admixtures. is calculated Rc* asis calculated reported by as Jolicouer reported etby al. Jolicouer [9] in Equation et al. [9] (1) in Equation (1) admixtures. Rc* is calculated as reported by Jolicouer et al. [9] in Equation (1) Rc* = RC/RC,NSF (1) Rc*Rc* = = R RC/RC/RC,NSFC,NSF (1)(1) where RC is the compressive strength measured for each admixture at each curing times and RC,NSF is where RC is the compressive strength measured for each admixture at each curing times and RC,NSF is wherethe compressive RC is the compressive strength measured strength for measured NSF3 at for 1, 7, each and admixture 28 days. Concrete at each curing manufactured times and with RC,NSF NSF3is the compressive strength measured for NSF3 at 1, 7, and 28 days. Concrete manufactured with NSF3 thegenerally compressive showed strength higher measuredcompressive for strength NSF3 at 1,values 7, and at 28 1 day days. with Concrete respect manufactured to ACR1 (see withFigure NSF3 7). generally showed higher compressive strengthstrength valuesvalues atat 11 dayday withwith respectrespect toto ACR1ACR1 (see(see FigureFigure7 ).7). 1.2 1.2 1.1 1.1 1 1 0.9 0.9 0.8 Rc* 0.8 NSF3 Rc* 0.7 NSF3 0.7 PNH1 PNH1 0.6 ACR1 0.6 ACR1 0.5 0.5 0.4 0.4 0 7 14 21 28 0 7 14 21 28 Time (day) Time (day)

Figure 7. Mean values of compressive strength (Rc* = RC/RC,NSF). FigureFigure 7. 7.Mean Mean values values of of compressive compressive strength strength (Rc* (Rc* = = R RCC/R/RC,NSF).). ACR1 admixture showed about a 10% decrease in the early compressive strength development ACR1 admixture showed about a 10% decrease in the early compressive strength development due ACR1to a side admixture effect of showedretardation about that a 10%occurs decrease in the case in the of early overdosage compressive due to strength incompatibility. development This due to a side effect of retardation that occurs in the case of overdosage due to incompatibility. This dueside toeffect a side is evident effect of only retardation at an early that age occurs and indisappears the case at of the overdosage age of 7 dueand to28 incompatibility.days when the side effect is evident only at an early age and disappears at the age of 7 and 28 days when the Thiscompressive side effect strength is evident becomes only at 2% an higher early age with and respect disappears to that at measured the age of on 7 and NSF 28‐superplasticized days when the compressive strength becomes 2% higher with respect to that measured on NSF‐superplasticized compressiveconcrete. Retardation strength prevails becomes on 2% the higher dispersing with respecteffect at to early that age, measured whereas on by NSF-superplasticized contrast at the age of concrete. Retardation prevails on the dispersing effect at early age, whereas by contrast at the age of concrete.7 and 28 days, Retardation dispersing prevails action on is thedominant dispersing and the effect retardation at early age,effect whereas becomes by negligible. contrast atPNH1 the 7 and 28 days, dispersing action is dominant and the retardation effect becomes negligible. PNH1 ageadmixture of 7 and evidenced 28 days, dispersingpoor compressive action isstrength dominant at 1 and day: the a mean retardation value effectof a 50% becomes decrease negligible. can be admixture evidenced poor compressive strength at 1 day: a mean value of a 50% decrease can be PNH1noticed admixture on all of the evidenced 13 analyzed poor cements compressive (see Figure strength 8). at 1 day: a mean value of a 50% decrease can noticed on all of the 13 analyzed cements (see Figure 8). be noticedThis fact on allcould of the be 13ascribed analyzed to the cements super (see‐retarding Figure 8effect). of the phosphonates [25] that causes a This fact could be ascribed to the super‐retarding effect of the phosphonates [25] that causes a prolonged induction period and, consequently, produces poor early age compressive strength. At the prolonged induction period and, consequently, produces poor early age compressive strength. At the Buildings 2017, 7, 62 8 of 10

This fact could be ascribed to the super-retarding effect of the phosphonates [25] that causes Buildings 2017, 7, 62 8 of 10 a prolongedBuildings 2017 induction, 7, 62 period and, consequently, produces poor early age compressive8 strength. of 10 At theage age of 7 ofand 7 28 and days, 28 a days,10% improvement a 10% improvement in compressive in strength compressive can be strengthevidenced can (see beFigure evidenced 9). age of 7 and 28 days, a 10% improvement in compressive strength can be evidenced (see Figure 9). (see FigureWhile 9the). While decrease the of decrease compressive of compressive strength may strength be attributed may be to attributed the retardation to the retardationinduced by inducedthe While the decrease of compressive strength may be attributed to the retardation induced by the by thephosphonate, phosphonate, connected connected to the to high the adsorption high adsorption energy and energy to the and reduced to the C3 reducedS dissolution C3S rate, dissolution the phosphonate, connected to the high adsorption energy and to the reduced C3S dissolution rate, the rate,higher the higher compressive compressive strength strength at later age at latershould age be shouldrelated to be the related microstructure to the microstructure of the hydration of the higher compressive strength at later age should be related to the microstructure of the hydration products. hydrationproducts. products. The variability of the compressive strength at early age is quite evident. Cements characterized The variabilityThe variability of the of the compressive compressive strength strength at at earlyearly age is is quite quite evident. evident. Cements Cements characterized characterized by a lower hydration kinetic and a low compressive strength development generally presented lower by aby lower a lower hydration hydration kinetic kinetic and a a low low compressive compressive strength strength development development generally generally presented presentedlower early‐age compressive strength with PNH‐based admixture; this is the case for concrete lowerearly early-age‐age compressive compressive strength strength with with PNH PNH-based‐based admixture; admixture; this thisis the is thecase casefor forconcrete concrete manufactured by using CEM II/B‐S 32.5R, CEM IV/A V 32.5R, CEM II/B‐LL 32.5 R (see Figure 8). manufacturedmanufactured by using by using CEM CEM II/B-S II/B‐S 32.5R, 32.5R, CEM CEM IV/AIV/A V V 32.5R, 32.5R, CEM CEM II/B II/B-LL‐LL 32.5 32.5 R (see R (seeFigure Figure 8). 8). PNH1 superplasticizer showed higher compressive strength at 1 day with cements with higher PNH1 superplasticizer showed higher compressive strength at 1 day with cements with higher PNH1strength superplasticizer class and rate showed of hardening. higher compressive The highest strengthcompressive at 1 strength day with at cements 1 day was with measured higher strength on strength class and rate of hardening. The highest compressive strength at 1 day was measured on classcement and rate belonging of hardening. to lot 3. This The might highest be related compressive to the higher strength fineness at of 1 daythese was cements, measured offsetting on the cement cement belonging to lot 3. This might be related to the higher fineness of these cements, offsetting the belongingretardation to lot induced 3. This by mightthe slower be C related3S dissolution. to the higher ﬁneness of these cements, offsetting the retardation induced by the slower C3S dissolution. retardation induced by the slower C3S dissolution.

1.4 1.4 1 day NSF3 ACR1 PNH1 1.2 1 day NSF3 ACR1 PNH1 1.2 1 1 0.8 0.8 Rc*

Rc* 0.6 0.6 0.4 0.4 0.2 0.2 0 0 CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM II/A IV III A II B-S II/A II/B IV/A II/A II/A IV/A II/A II/B IV/A II/A IV III A II B-S II/A II/B IV/A II/A II/A IV/A II/A II/B IV/A LL A/P 32.5 N32.5 R LL LL V 32.5 LL LL V 42.5 LL LL V 32.5 LL A/P 32.5 N32.5 R LL LL V 32.5 LL LL V 42.5 LL LL V 32.5 42.5 R42.5 R 42.5 R32.5 R R 42.5 R32.5 R R 42.5 R32.5 R R 42.5 R42.5 R 42.5 R32.5 R R 42.5 R32.5 R R 42.5 R32.5 R R Lot1 Lot2 Lot3 Lot4 Lot1 Lot2 Lot3 Lot4

Figure 8. Normalized compressive strength at 1 day. FigureFigure 8. 8.Normalized Normalized compressive compressive strength strength at at 1 day. 1 day.

60 60 NSF3 ACR1 PNH1 28 days NSF3 ACR1 PNH1 50 28 days 50 40 40 30 30 Rc (MPa)

Rc (MPa) 20 20 10 10 0 0 CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM CEM II/A IV III A II B-S II/A II/B IV/A II/A II/A IV/A II/A II/B IV/A II/A IV III A II B-S II/A II/B IV/A II/A II/A IV/A II/A II/B IV/A LL A/P 32.5 N32.5 R LL LL V 32.5 LL LL V 42.5 LL LL V 32.5 LL A/P 32.5 N32.5 R LL LL V 32.5 LL LL V 42.5 LL LL V 32.5 42.5 R42.5 R 42.5 R32.5 R R 42.5 R32.5 R R 42.5 R32.5 R R 42.5 R42.5 R 42.5 R32.5 R R 42.5 R32.5 R R 42.5 R32.5 R R Lot1 Lot2 Lot3 Lot4 Lot1 Lot2 Lot3 Lot4

Figure 9. Compressive strength at 28 days. Figure 9. Compressive strength at 28 days. Figure 9. Compressive strength at 28 days. Buildings 2017, 7, 62 9 of 10

4. Conclusions A new phosphonate-based superplasticizer was synthetized by using amino-methane phosphonic polymer. Rheological and mechanical behaviors of concrete manufactured with superplasticizers belonging to NSF and PCE families and a new experimental phosphonate-based admixture were compared. The experimental tests were carried out on 13 different cement type/strength classes from three different cement producers to evaluate the superplasticizer compatibility. Experimental data collected showed that the new synthetized phosphonate-based superplasticizer is characterized by:

• higher efﬁciency in terms of water reduction with respect to NSF product, but lower than PCE-based admixtures; • lower dosage variability for mixes made with different types of cement and strength classes, with respect to both PCE and NSF-based admixtures; • higher workability retention at 60 min with respect to both PCE-based and NSF-based admixtures; • lower workability change upon cement type/strength class with respect to both PCE and NSF products; • no anomalous air-entrapping tendency; • improvement of compressive strength at one day is relative in comparison to those at 7 and 28 days.

Despite phosphonate-based admixture showing lower efﬁciency with respect to PCE-based admixtures, higher compatibility of different cement was evidenced in terms of dosage and workability retention. The results are promising and an increasing interest in the study of this kind of admixture is expected.

Author Contributions: L.C. and S.L. conceived and designed the experiments; S.L. performed the experiments; S.L. and P.K. analyzed the data and managed the literature searches; S.G. contributed reagents/materials/analysis tools; L.C. wrote the first draft of the paper. Conflicts of Interest: The authors declare no conflict of interest.

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