Influence of Water to Cement Ratio with Different Amount of Binder on Properties of Ultra-High Performance Concrete

Four different compositions of ultra-high performance concrete (UHPC) have been created for this study, while W/C ratio varied from 0.25 to 0.33. Amount of cement, quartz sand and super plasticizer has been maintained constant (at 735 kg/m3, 962 kg/m3 and 36.76 l respectively). Glass powder and silica fume were used as binder. Optimal fineness of glass powder was selected by Chapelle test. In this study different combinations of silica fume, glass powder and quartz powder as microfiller were used. Compressive strength up to 160 MPa was obtained. The main aim of experiment was to create relationships between w/c ratio and compressive strength and to find optimal composition of UHPC. Test methods such as: slump, dynamic viscosity, density, and compressive strength were used. In experiment glass powder was successfully utilized in UHPC.


Introduction
and ternary compound pastes containing silica fume (SF), pulverized granulated blast furnace slag (PS) and pulverized fly ash (PFA).He stated that SF is more effective in improving the packing density of cement matrix, because silica fume has positive effect on interfiling spaces between larger particles.Sobolev et al. 2004 proposed a new method to design and optimize concrete mixture.In experiment he replaced part of cement by various mineral addictive's.According to research workability of UHPC can be modified by different amount of super plasticizer (from 5% up to 10% by weight of cement) and by different amount of silica fume (from 5 % up to 25 % by weight of cement).However particle size distribution also has important role.Amen et al. 2011 studied compressive strength of UHPC development with different amount of silica fume.He founded that silica fume has positive effect on early and later compressive strength of concrete.Moghadam et al. 2012 founded that with decreased W/C ratio most of mechanical properties will improve and porosity will decrease.The similar findings were made by Rahmani et al. 2012.He also noticed that with decreased W/C ratio also increased resistance to abrasion can be observed.
Microstructural investigations conducted by Reda et al. 1999 with SEM micrographs, pointed out the reason why UHPC differs from conventional concrete.In fact, it is believed that the mixture containing SF and silica flour (a pulverized quartz of a uniform size <75 µm) together with the low W/B ratio leads to a very dense and homogeneous microstructure, with a very low porosity, which impede the formation of the large crystals of CH (that, in fact, are generally absent in UHPC).It has been noticed in some specimens that a relatively high content of silica fume, together with the inclusion of silica flour and the elevated temperature curing regime, created an effective pozzolanic environment which consumed most of the weak CH crystals produced during hydration.These crystals were converted in to strong C-S-H, and so excellent mechanical properties occurred.Alawode et al. 2011 founded that in the concrete with high W/C ratio, CH crystals tend to grow larger comparing with low W/C ratio mixtures.
The effect of recycled glass powder (GP) on the slump and compressive strength in ultra-high performance fibre reinforced concrete (UHPFRC) has been studied by Kou et al. 2012.In this experiment the cement was partially replaced by the glass powder and the amount of silica fume was kept constant.The results revealed that glass powder reduced the flow ability of fresh UHPFRC.As a matter of fact, the workability of concrete decreased with an increase in amount of glass powder.It has been also founded out that, by replacing cement with GP, the 7 days-compressive tend to decrease, while the later compressive strength (after 28 days) tend to increase.Similar conclusions have been made by Khatib et al. 2012.He noticed that optimal amount of glass powder is when 10 % of cement is replaced by glass powder, however when substitution degree is above 20 %, the compressive strength tends to decrease.Patil et al. 2013 also agrees that addition of GP increases the strength of concrete.His experiments underline that in 7 days glass powder give less strength, this probably due to low hydration process.Abdelalim et al. 2008 stated that when W/C ratio varies from 0.15 to 0.17 optimal amount of silica fume is between 10 % and 15 % of cement mass.However not all silica reacts chemically with portlandite, some of it remains unreacted and fills empty voids, between larger particles.Tavakoli et al. 2013 found that above 15 % of silica fume of cement mass tends to decrease workability of concrete.
According to the literature there are not so many results pointing out how exactly W/C ratio influences mechanical properties of UHPC.How glass powder affects workability and compressive strength of UHPC.Some authors state that glass powder can increase workability and compressive strength of concrete while others think differently.It is not clear which amount of glass powder is optimal in UHPC system.In order to clarify misconception four different composition of ultrahigh performance concrete (UHPC) have been created for this study, while W/C ratio varied from 0.25 to 0.33.The main aim of experiment was to create relationships between w/c ratio and compressive strength and to find optimal composition of UHPC.Test methods such as: slump, dynamic viscosity, density, and compressive strength were used.Silica fume.Silica fume, also known as microsilica (MS) or condensed silica fume is a by-product of the production of silicon metal or ferrosilicon alloys.Main properties: density -2532 kg/m 3 ; bulk density -400 kg/m 3 ; pH -5.3.Particle size distribution is shown in Fig. 1.
Quartz powder.In experiment quartz powder was used.Main properties: density 2650 kg/m 3 ; bulk density -900 kg/m 3 ; average particle size -18.12µm; specific surface (by Blaine) -6543 cm 2 /g.Particle size distribution is shown in Fig. 2.  Glass powder.In experiment glass powder was made from various colour bottles.Bottles were crushed in ball miller and milled until certain fineness.Main properties: density 2528 kg/m 3 ; specific surface (by Blaine) -varied from 2119 cm 2 /g to 7399 cm 2 /g with optimal value of 5240 cm 2 /g.Particle size distribution is shown in Fig. 2.

Used materials
Quartz sand.In experiment quartz sand was used.Main properties: fraction: 0/0.5; density 2650 kg/m 3 ; specific surface (by Blaine) -91 cm 2 /g.According to the methods described before, four compositions of UHPC with different amounts of binder were created (Table 2).Silica fume and glass powder were used as binder.Water to cement ratio (W/C) in all compositions varied from 0.25 to 0.32.QP/GP0-SiO 2 /GP0 is as reference composition, without any pozzolanic material; QP/GP0 is standard UHPC composition with silica fume; QP/GP100 when 100 % quartz powder was substituted by glass powder.In QP/GP100SF/ GP100 quartz powder and silica fume were substituted by 100 % of glass powder and in SF/GP100 silica fume was substituted by 100 % of glass powder.For investigation slump, dynamic viscosity, density, and compressive strength test methods were used.Main aim of the experiment was to find relationship between W/C and compressive strength.Properties of UHPC were obtained with and without heat treatment.

Results
Fig. 3 Results of Chapelle test for glass powder and silica fume

Optimal fineness of glass powder
According to Chapelle test (Fig. 3), the pozzolanic reactivity is evaluated on the basis of the amount of Ca(OH) 2 consumed during the pozzolanic reaction.
Experiment results indicate that pozzolanicity of glass powder after it oversteps fineness of 5240 cm 2 /g tends to increase insignificantly.When fineness of glass powder varies from 2119 cm 2 /g to 7399 cm 2 /g consumed amount of Ca(OH) 2 varies from 465 mg to 652 mg respectively.
Optimal fineness of glass powder according to the consumed amount of Ca(OH) 2 is 5240 cm 2 /g.The same amount of silica fume consumes 1536 mg of Ca(OH) 2 and it is almost 3 times more reactive than glass powder.In Fig. 3 specific surface of silica fume is not presented, because Blaine test method shows inaccurate results.Specific surface of silica fume usually varies from 15000 m 2 / kg to 30000 m 2 /kg by BET test method.

Slump and dynamic viscosity
As was expected, the increase of W/C ratio resulted in increase of

Fig. 4
Relationship between water to cement ratio and slump mixture's slump.Regardless if was used or not any pozzolanic material, but slump in all composition was almost the same and varied from 24 cm to 42 cm (Fig. 4).The lowest dynamic viscosity was noticed in composition (GP/GP100 SiO 2 /GP100) when 100 % of glass powder and 100 % of silica fume were substituted by glass powder.
When W/C varied from 0.25 to 0.33 dynamic viscosity varied 202 Pa•s to 57 Pa•s respectively with optimal value of 57 Pa•s at W/ C=0.27 (Fig. 5).Decreased dynamic viscosity probably could be attributed due to better particle size distribution and due to lower specific surface area of glass powder comparing with quartz powder and silica fume.

Density and compressive strength
As it was expected density in all compositions with and without thermal treatment was very similar and it was about 2400 kg/m 3 .The density of UHPC by thermal treatment was not significantly influenced (Fig. 6 and Fig. 7).
Slightly decreased density probably could be attributed due to higher amount of evaporable water which tends to increase capillary porosity of concrete and thus decrease overall density.It seems that glass powders does not influence overall density of UHPC or the influence it insignificant.
The lowest compressive strength was obtained in composition (QP/ GP0 SiO 2 /GP0) without heat treatment and without any pozzolanic additive.When W/C varied from 0.25 to 0.33 compressive strength varied from 114 MPa to 94 MPa respectively (Fig. 8).

Fig. 5
Relationship between water to cement ratio and dynamic viscosity

Fig. 6
Relationship between water to cement ratio and density when heat treatment was not applied Fig. 7 Relationship between water to cement ratio and density when heat treatment (3+16+5) for 24 hours in 80 °C was applied The highest compressive strength was noticed in composition (QP/ GP100) with silica fume and when 100 % of quartz powder was substituted by glass powder.When W/C varied from 0.25 to 0.33 compressive strength varied from 145 MPa to 119 MPa respectively.After thermal treatment compressive strength increased even more (Fig. 9).

Very
good results were noticed in composition (QP/ GP100SiO 2 GP100) where 100 % of quartz powder and 100 % of silica fume were substituted by glass powder.When heat treatment was not applied in composition QP/ GP100SiO2GP100 compressive strength varied from 124 MPa (W/ C=0.25) to 101 MPa (W/C=0.33)and it is similar as in ordinary UHPC composition (QP/GP0) without glass powder.However after heat treatment in composition (QP/ GP100SiO 2 GP100) where 100% of quartz powder and 100 % of silica fume were substituted to glass powder, compressive strength greatly increased.In experiment was noticed, that glass powder could be properly incorporated in Fig. 8 Relationship between water to cement ratio and compressive strength when heat treatment was not applied

Fig. 9
Relationship between water to cement ratio and compressive strength when heat treatment (3+16+5) for 24 hours in 80 °C was applied UHPC without any loss of compressive strength and thus overall price of concrete can be decreased.
Article analyses very important problem, how properly dispose waste glass.Milled glass can be successfully utilised in UHPC and used instead of silica fume or quartz powder.An eliminated expensive material has great benefit in reducing cost of UHPC.Such experiment is novelty in Lithuania and until now it has not done at all.
Extensive experiment was carried out to create optimal composition of UHPC when different amount of glass powder in the mixture were incorporated.The following conclusions can be derived from the present investigation: 1 Optimal fineness of glass powder according to the consumed amount of Ca(OH) 2 is 5240 cm 2 /g.Further reducing the fineness of glass powder is not optimal.
2 The best compressive strength (164 MPa) results were obtained in mixture with silica fume and when 100 % of quartz powder was substituted by glass powder.

Fig. 2
Fig. 2Particle size distribution of glass powder