MÓDULO VIII: PRÁCTICAS II:
3.3 MÉTODO DE DISEÑO, IMPLEMENTACIÓN Y EVALUACIÓN DE LAS UNIDADES DE MEDIACIÓN SANITARIA (UMS)
3.3.6 Plan de comunicación del proyecto
Table 4.5: Mix Design Four
Materials kg/m3 kg
20 mm 554 39
10 mm 277 19
7 mm 462 32
Sand 554 39
Fly Ash 408 29
Sodium Silicate 103 7.2 Sodium Hydroxide 41 2.9
Silica Fume -
-Calcium Hydroxide -
-Extra Water -
-TOTAL 2400 168.0 MIX FOUR
An investigation into the effect of raising the free water content of a geopolymer concrete mix was carried out. This undertaken research was required to distinguish between the method of producing geopolymer paste and concrete. The included aggregate in the concrete holds water and therefore a workable concrete mix can be made without the addition of any extra water to the mix.
Avoiding this condition can be achieved by preparing the aggregate in Saturated Surface Dry condition. This was not carried out in an attempt to keep the research relevant to large scale concrete production, in which it would not be efficient to prepare large quantities of aggregates to SSD. It is also a difficult stage to get to, as it is based on visual and touch parameters, however it can be complied with by Australian Standard 1141.5‐2000 and 1141.6.1‐2000. The concept of preparing aggregate to SSD is that the particles appear damp, but upon surface touching no moisture is felt and therefore would occur differently upon individual opinion. This condition is optimum for concrete preparation in order to yield aggregate that is holding enough moisture only to a point where it is not surface wet, and therefore not
contributing any water to the mix. The moisture of these particles also prevents any of 65 litre mix of concrete, including 1.5 litres of extra added water, producing a 2.6%
free water content as seen in Table 4.6. By using aggregate that was not prepared in any situation obtaining it straight from the outside conditions under the rain, Mix Four’s water content was raised to 4.2% after calculating 6.5 litres of free water in the aggregate and alkaline solution as seen in Table 4.7.
Prior to mixing, it was anticipated that the strength of this mix with the higher free water content would be lower than Mix One. This is the situation as seen in ordinary
20mm 0.45 36 0.16
10mm 0.69 18 0.12
7mm 1.64 30 0.49
Sand 0.42 36 0.15
Added Water 1.5
Mix Four (investigating a mix with a higher water content) was designed exactly the same as Mix One poured earlier in the year. No preparation of the aggregates was carried out as these were obtained straight from the storage area, that was exposed to heavy rain that week, into sealed bins to retain the water content at that time.
It was noticed that the water in the mix had an effect on the appearance of the geopolymer concrete. The concrete had an oily appearance with black portions spread throughout where the excess water was sitting in the mix. Figure 4.9 below shows an example of this on top of a poured cylinder during the placement. These black sections disappeared as the concrete set. This oily appearance was seen consistently over all further mixes produced with this high free water content throughout the year.
20mm 1.25 36 0.45
10mm 1.50 18 0.27
7mm 4.14 30 1.24
Sand 8.17 36 2.94
Added Water 0
Figure 4.9: Excess Water in Geopolymer Concrete
Obviously, when mixed the concrete was exceptionally easy to place with the high water content and the mix had a high slump value of over 250mm. Due to the high slump nature of this mix, only a light amount of vibration was applied to the cylinders to avoid segregation of the mix and letting all the aggregate fall to the bottom of the moulds and therefore producing more of a paste at the top of the cylinder.
Understandably, Mix Four took quite some time to set. At 7 days old it was seen that the concrete still may not have set properly, as the strength at this time was even lower than expected, with a 2.5 MPa average in comparison to Mix One’s 8.6 MPa. Mix Four only had specimens taken for 7 and 28 days old in compression, and 28 days for tensile. Therefore, the strength development and rate of changes cannot be observed as closely over 28 days.
The final strength of Mix Four did not get close at all to Mix One as seen in Figure 4.10.
At 28 days the compressive strength of concrete reached 10.8 MPa (Table 4.8). It can
therefore be seen that by increasing the free water content in a geopolymer mix to
Compressive Strength (MPa)
Age After Pouring (Days)
Compressive Strength of Geopolymer Concrete (MPa)
Mix One
4.3.3 The Use of Calcium Hydroxide to Aid Ambient Curing
Table 4.9: Mix Design Three
Materials kg/m3 kg
20 mm 554 36
10 mm 277 18
7 mm 462 30
Sand 554 36
Fly Ash 380 25 Sodium Silicate 103 6.7 Sodium Hydroxide 41 2.7
Silica Fume -
-Calcium Hydroxide 28 1.8
Extra Water -
-TOTAL 2400 156.0 MIX THREE
Due to the high moisture content of the aggregates used, the concrete mix was extremely wet during mixing. At this point it would be thought that placement of the
ash and the calcium hydroxide. At this point it was realized that something never experienced by the author was occurring so progress was made as quick as possible to place the concrete into the moulds.
Approximately ten minutes into placement of the concrete in the moulds, rapid setting began to occur and placement of the mix became very difficult. Vibration of the cylinders did not have an effect on the form of the concrete, and air voids remained in some of the cylinders. Because the concrete was set on the day of casting, de‐
moulding of the cylinders was carried out at only two days of age. Upon removing the concrete from the moulds it was apparent that majority of the compression cylinders turned out fine for testing as usual. The tensile cylinders on the other hand, appeared to have a considerable amount of voids in them because of the fast setting concrete, however testing of these cylinders was still carried out in order to yield some data for this mix (Figure 4.12).
Mix Three and Four were produced on the same day and therefore had the same relatively high free water content. Mix Four, as explained in the previous section of this report, is a standard geopolymer concrete mix investigating the effect of high water content. For this reason, Mix Three and all further mixes later on in the year were compared to Mix Four. The strength of Mix Three was consistently stronger than the reference mix throughout, and the rate of strength development was substantially larger up until 14 days of age. Eventually, though, the strength development of Mix Three tapered off and did not exhibit any rapid strength gain within 28 days. The final testing at 28 days showed a compressive strength of 18 MPa, comparative to Mix Four which exhibited a 28 day strength of 11 MPa as seen in Table 4.10 and Figure 4.11.
Compressive Strength (MPa)
Age After Pouring (Days)
Compressive Strength of Geopolymer Concrete (MPa)
Mix One
Figure 4.12 : Rapid Setting Effects and Efflorescence on Mix Three Cylinders
Figure 4.13: Cross Section of Small Cylinder ‐ Mix Three
Figure 4.13 shows the cross section of a cylinder from Mix Three. The most obvious aspect is the shape of the top (right side of the image) where the concrete had set just as the cylinder had been filled up. The material at the top of these cylinders was flaky and brittle and so each affected cylinder had this surface condition trimmed off prior to testing. Another aspect of this cylinder is the amount of air voids seen throughout the section. Because Mix Three set whilst the cylinders were being vibrated all of the air voids were not able to be removed from the concrete.
It should however be noted, that any results obtained from the testing of these specimens provide little use in further applications of geopolymer concrete mix design.
It is recommended that the research in the addition of calcium hydroxide is continued with varying amounts added. On a larger scale in industry the time for placement of concrete would be much longer, and therefore setting would occur before all concrete is put into place. However, for the purpose of this research, the strength development is to be investigated into the addition of calcium hydroxide to geopolymer concrete, so testing of the cylinders continued.
As seen in Figure 4.12 Mix Three also exhibited an amount of efflorescence on the outside of the cylinders. It was apparent at this stage that all geopolymer concrete samples cured under ambient conditions consistently exhibited this property.
Approximately a week later, it was informed to the author of this report, that the Physics department at Curtin University had attempted to replicate the rapid setting nature of this mix by producing a geopolymer paste mix with the same proportions as Mix Three, albeit without the aggregate. The outcome, however, differed in that the mix did not rapid set whilst preparing and in fact took approximately 36 hours before it had properly set (M. Lee, personal communication August 26, 2009).
To further the research into the effect of adding calcium hydroxide to geopolymer concrete, Mixes Five, Six and Seven were produced with varying amounts of the
set mix as an addition, not through substitution for fly ash. This was achieved by producing a replica of Mix Four (standard geopolymer concrete mix, with high water content, as was Mix Three) and adding the hydrated lime at a percentage by mass of the geopolymer paste in the concrete. Quantities of 0.5%, 1% and 3% of the geopolymer were added to the concrete mix respectively. Table 4.11 below shows the specific mix designs of these mixes. It can be seen that the total composition of Mixes Five to Seven exceed a composition of 2400 kg/m3 due to the extra water and calcium hydroxide added to the already complete concrete mix. The amount of water added was calculated in order to yield the same free water content as Mixes Three and Four.
Table 4.11: Mix Designs Five, Six and Seven
Materials kg/m3 kg kg/m3 kg kg/m3 kg
20 mm 554 5.5 554 5.5 554 5.5
10 mm 277 2.8 277 2.8 277 2.8
7 mm 462 4.6 462 4.6 462 4.6
Sand 554 5.5 554 5.5 554 5.5
Fly Ash 408 4.1 408 4.1 408 4.1
Sodium Silicate 103 1.0 103 1.0 103 1.0
Sodium Hydroxide 41 0.4 41 0.4 41 0.4
Silica Fume - - - - -
-Calcium Hydroxide 2.8 0.03 5.5 0.1 17 0.2
Extra Water 96 1.0 96 1.0 96 1.0
TOTAL 2499 25.0 2502 25.0 2513 25.1 MIX FIVE MIX SIX MIX SEVEN
In order to avoid quick setting mixes hardening in the pan, the bulk standard mix design was produced and then the required amount for each sub‐mix (Mixes Five, Six and Seven) was placed onto an aggregate preparation tray. From here the varying amounts of calcium hydroxide was added and then mixed by hand into the concrete.
This also allowed for a better feel of the workability of the mix, as any quick setting could be detected straight away.
Mix Five (0.5% calcium hydroxide) presented no difference in workability or immediate setting time whilst mixing compared to Mix Four. In order to make the required amount of concrete for 6 compression cylinders (3 x 7 days, 3 x 28 days), only 29 grams of calcium hydroxide was added to 25 kilograms of concrete. In the time it took to mix
in the calcium hydroxide and then transfer the concrete into the cylinders, Mix Five appeared to have no difference in workability relative to any standard geopolymer mix prepared earlier in the year. After 24 hours of curing it was apparent that Mix Five had still not set. Complete setting occurred by 5 days after pouring, very similar to a standard geopolymer concrete mix with no additives.
Mix Six (1% calcium hydroxide) exhibited a slightly faster setting rate than Mix Five during the day. An amount of 58 grams of calcium hydroxide was added to the concrete mix and whilst there was no noticeable setting or difference in workability during placement, approximately two hours after producing the mix it was clear that it had begun setting. Figure 4.14 below shows the excess of Mix Six at two hours after mixing and partially set. At this point the concrete was beginning to harden on the top, however beneath the surface it was still very wet. By 3 days of curing Mix Six had completely set and was able to be removed from the moulds.
Figure 4.14: Mix Six at Two Hours after Pouring
Mix Seven (3% calcium hydroxide) was the only mix prepared out of the last three which exhibited noticeable early setting properties during placement of the concrete.
It was experienced that whilst combining the 173 grams of calcium hydroxide that the workability of the concrete changed almost instantly, however not enough to affect the placement. The mix felt heavier to move after mixing in the calcium hydroxide as it appeared the reaction between the chemicals in the concrete had occurred immediately. The rate of reaction was not as quick as Mix Three though, where the concrete set before all cylinders could be poured, and therefore the placement of Mix Seven went accordingly to plan.
Again, the left over concrete from Mix Seven was kept to observe how long it took to set compared to Mix Six. After just one hour Mix Seven was significantly harder than Mixes Five and Six, and was obviously going to be completely set within hours. Figure 4.15 below shows the condition of the excess from Mixes Six and Seven after one hour of setting, and it can be seen that Mix Six is still completely wet where as Mix Seven is significantly further along in the setting process. After twelve hours of standing after pouring, Mix Seven had completely set and therefore the cylinders would have been able to be de‐moulded after 24 hours.
Figure 4.15: Mixes Seven (Left) and Six (Right) at One Hour after Pouring
The relatively low final strength’s of Mixes Five, Six and Seven came as quite unexpected due to the setting times experienced by the three mixes. Though Mix Five set in the same amount of time as the reference mix, it was expected that a small amount of calcium hydroxide would have a compressive strength slightly higher, if not equal to the reference Mix Four. The faster setting nature of Mixes Six and Seven made for the prediction of higher compressive strengths in proportion to the amount of calcium hydroxide used. Despite this, the highest compressive strength experienced by
Compressive Strength (MPa)
Age After Pouring (Days)
Compressive Strength of Geopolymer Concrete (MPa)
Mix One
It can be seen from the results in Table 4.12 that the compressive strength of geopolymer concrete increases in proportion to the amount of calcium hydroxide used within the mix. Mix Seven with a 3% calcium hydroxide addition exhibited a slightly higher compressive strength than Mixes Five and Six. The difference though is seen at the 7 day strengths where any addition of calcium hydroxide to a geopolymer concrete mix increases the strength and rate of setting, making the mix applicable for use in industry applications where the concrete is cured without the use of steam rooms. equal to a mix without any additives. If Mix Seven had achieved a final compressive strength substantially higher than the reference mix, it would be seen that this was the
It was interesting to discover the substantial difference between a 3% addition of calcium hydroxide relative to the 5% replacement of fly ash as seen in Mix Three.
Despite the fact that Mix Three was deemed a failure, the compressive strengths of the unaffected cylinders were still substantial. From this, it would be seen that incorporating a 3% replacement of fly ash with calcium hydroxide would produce a mix that sets within 12 hours and presents positive compressive and tensile strengths.
Figure 4.17: Efflorescence Beginning to Form after De‐moulding ‐ Mix Five
4.4 Indirect Tensile Strength of Geopolymer Concrete
The relationship between the compressive strength and indirect tensile strength of concrete is well known. Whilst not as heavily relied upon from the results point of view, the tensile strength of the tested specimens must also be analysed to gain a full perspective of the conclusions. The tensile strength of these specimens was tested in compliance with Australian Standard 1012.10‐2000.