International Science Index
Effect of Sodium Aluminate on Compressive Strength of Geopolymer at Elevated Temperatures
Geopolymer is an inorganic material synthesized by alkali activation of source materials rich in soluble SiO2 and Al2O3. Many researches have studied the effect of aluminum species on the synthesis of geopolymer. However, it is still unclear about the influence of Al additives on the properties of geopolymer. The current study identified the role of the Al additive on the thermal performance of fly ash based geopolymer and observing the microstructure development of the composite. NaOH pellets were dissolved in water for 14 M (14 moles/L) sodium hydroxide solution which was used as an alkali activator. The weight ratio of alkali activator to fly ash was 0.40. Sodium aluminate powder was employed as an Al additive and added in amounts of 0.5 wt.% to 2 wt.% by the weight of fly ash. The mixture of alkali activator and fly ash was cured in a 75°C dry oven for 24 hours. Then, the hardened geopolymer samples were exposed to 300°C, 600°C and 900°C for 2 hours, respectively. The initial compressive strength after oven curing increased with increasing sodium aluminate content. It was also observed in SEM results that more amounts of geopolymer composite were synthesized as sodium aluminate was added. The compressive strength increased with increasing heating temperature from 300°C to 600°C regardless of sodium aluminate addition. It was consistent with the ATR-FTIR results that the peak position related to asymmetric stretching vibrations of Si-O-T (T: Si or Al) shifted to higher wavenumber as the heating temperature increased, indicating the further geopolymer reaction. In addition, geopolymer sample with higher content of sodium aluminate showed better compressive strength. It was also reflected on the IR results by more shift of the peak position assigned to Si-O-T toward the higher wavenumber. However, the compressive strength decreased after being exposed to 900°C in all samples. The degree of reduction in compressive strength was decreased with increasing sodium aluminate content. The deterioration in compressive strength was most severe in the geopolymer sample without sodium aluminate additive, while the samples with sodium aluminate addition showed better thermal durability at 900°C. This is related to the phase transformation with the occurrence of nepheline phase at 900°C, which was most predominant in the sample without sodium aluminate. In this work, it was concluded that sodium aluminate could be a good additive in the geopolymer synthesis by showing the improved compressive strength at elevated temperatures.
Characteristic on Compressive Strength of Blast Slag and Fly Ash Hybrid Geopolymer Mortar
Geopolymer mortar is produced by alkaline activation of pozzolanic materials such as fly ground granulated blast-furnace slag (GGBFS) and fly ash (FA). Its unique reaction pathway facilitates rapid strength development in comparison with hydration of ordinary Portland cement (OPC). Geopolymer can be fabricated using various types and dosages of alkali-activator, which effectively gives a wider control over the performance of the final product. The present study investigates the effect of types of precursors and curing conditions on the fresh state and strength development characteristics of geopolymers, thereby comparatively exploring the effect of precursors from various sources of origin. The obtained result showed that the setting time and strength development of the specimens with the identical mix proportion but different precursors displayed significant variations.
Study of Metakaolin-Based Geopolymer with Addition of Polymer Admixtures
In the present work, metakaolin-based geopolymer including different polymer admixtures was studied. Different types of commercial polymer admixtures VINNAPAS® and polyethylene glycol of different relative molecular weight were used as polymer admixtures. The main objective of this work is to investigate the influence of different types of admixtures on the properties of metakaolin-based geopolymer mortars considering their different dosage. Mechanical properties, such as flexural and compressive strength were experimentally determined. Also, study of the microstructure of selected specimens by using a scanning electron microscope was performed. The results showed that the specimen with addition of 1.5% of VINNAPAS® 7016 F and 10% of polyethylene glycol 400 achieved maximum mechanical properties.
Investigation of the Recycling of Geopolymer Cement Wastes as Fine Aggregates in Mortar Mixes
Fly ash-slag based Geopolymer Cement (GPC) is presenting mechanical properties and environmental advantages that make it the predominant “green” alternative to Portland Cement (PC). Although numerous life-cycle analyses praising its environmental advantages, disposal after the end of its life remains as an issue that has been barely explored. The present study is investigating the recyclability of fly ash-slag GPC as aggregate in mortars. The purpose of the study was to evaluate the effect of GPC fine Recycled Aggregates (RA), at replacement levels of 25% and 50%, on the main mechanical properties of PC and GPC mortar mixes. The results were compared with those obtained by corresponding mixes incorporating natural and PC-RA. The main physical properties of GPC-RA were examined and proven to be comparable to those of PC-RA and slightly inferior to those of natural sand. A negligible effect was observed at 28-day compressive and flexural strength of PC mortars with GPC aggregates having a milder effect than PC. As far as GPC mortars are concerned, the influence of GPC aggregates was enhancing for the investigated mechanical properties. Additionally, a screening test showed that recycled geopolymer aggregates are not prone of inducing alkali silica reaction.
Experimental Study on Flexural Strength of Reinforced Geopolymer Concrete Beams
This paper presents the flexural response of Reinforced Geopolymer Concrete (RGPC) beams. A commercial finite element (FE) software ABAQUS has been used to perform a structural behavior of RGPC beams. Using parameters such: stress, strain, Young’s modulus, and Poisson’s ratio obtained from experimental results, a beam model has been simulated in ABAQUS. The results from experimental tests and ABAQUS simulation were compared. Due to friction forces at the supports and loading rollers; slip occurring, the actual deflection of RGPC beam from experimental test results were slightly different from the results of ABAQUS. And there is good agreement between the crack patterns of fly ash-based geopolymer concrete generated by FE analysis using ABAQUS, and those in experimental data.
Effect of Alkaline Activator, Water, Superplasticiser and Slag Contents on the Compressive Strength and Workability of Slag-Fly Ash Based Geopolymer Mortar Cured under Ambient Temperature
Geopolymer (cement-free) concrete is the most promising green alternative to ordinary Portland cement concrete and other cementitious materials. While a range of different geopolymer concretes have been produced, a common feature of these concretes is heat curing treatment which is essential in order to provide sufficient mechanical properties in the early age. However, there are several practical issues with the application of heat curing in large-scale structures. The purpose of this study is to develop cement-free concrete without heat curing treatment. Experimental investigations were carried out in two phases. In the first phase (Phase A), the optimum content of water, polycarboxylate based superplasticizer contents and potassium silicate activator in the mix was determined. In the second stage (Phase B), the effect of ground granulated blast furnace slag (GGBFS) incorporation on the compressive strength of fly ash (FA) and Slag based geopolymer mixtures was evaluated. Setting time and workability were also conducted alongside with compressive tests. The results showed that as the slag content was increased the setting time was reduced while the compressive strength was improved. The obtained compressive strength was in the range of 40-50 MPa for 50% slag replacement mixtures. Furthermore, the results indicated that increment of water and superplasticizer content resulted to retarding of the setting time and slight reduction of the compressive strength. The compressive strength of the examined mixes was considerably increased as potassium silicate content was increased.
Utilization of Nanoclay to Reinforce Flax Fabric-Geopolymer Composites
Geopolymer composites reinforced with flax fabrics
and nanoclay are fabricated and studied for physical and mechanical
properties using X-Ray Diffraction (XRD), Fourier Transform
Infrared Spectroscopy (FTIR), and Scanning Electron Microscope
(SEM). Nanoclay platelets at a weight of 1.0%, 2.0%, and 3.0% were
added to geopolymer pastes. Nanoclay at 2.0 wt.% was found to
improve density and decrease porosity while improving flexural
strength and post-peak toughness. A microstructural analysis
indicated that nanoclay behaves as filler and as an activator
supporting geopolymeric reaction while producing a higher content
geopolymer gel improving the microstructure of binders. The process
enhances adhesion between the geopolymer matrix and flax fibres.
Characteristics of Nanosilica-Geopolymer Nanocomposites and Mixing Effect
This paper presents the effects of mixing procedures
on mechanical properties of flyash-based geopolymer matrices
containing nanosilica (NS) at 0.5%, 1.0%, 2.0%, and 3.0% by weight.
Comparison is made with conventional mechanical dry-mixing of NS
with flyash and wet-mixing of NS in alkaline solutions. Physical and
mechanical properties are investigated using X-Ray Diffraction
(XRD) and Scanning Electron Microscope (SEM). Results show that
generally the addition of NS particles enhanced the microstructure
and improved flexural and compressive strengths of geopolymer
nanocomposites. However, samples, prepared using dry-mixing
approach, demonstrate better physical and mechanical properties
comparing to wet-mixing samples.
Effect of Local Steel Slag as a Coarse Aggregate on Properties of Fly Ash Based-Geopolymer Concrete
Local steel slag is produced as a by-product during the
oxidation of steel pellets in an electric arc furnace. Using local steel
slag waste as a hundred substitutes of crashed stone in construction
materials would resolve the environmental problems caused by the
large-scale depletion of the natural sources of crashed stone. This
paper reports the experimental study to investigate the influence of a
hundred replacement of crashed stone as a coarse aggregate with
local steel slag, on the fresh and hardened geopolymer concrete
properties. The investigation includes traditional testing of hardening
concrete, for selected mixes of cement and geopolymer concrete. It
was found that local steel slag as a coarse aggregate enhanced the
slump test of the fresh state of cement and geopolymer concretes.
Nevertheless, the unit weight of concretes was affected. Meanwhile,
the good performance was observed when fly ash used as geopolymer
Effect of Crashed Stone on Properties of Fly Ash Based-Geopolymer Concrete with Local Alkaline Activator in Egypt
Green concrete are generally composed of recycling
materials as hundred or partial percent substitutes for aggregate,
cement, and admixture in concrete. To reduce greenhouse gas
emissions, efforts are needed to develop environmentally friendly
construction materials. Using of fly ash based geopolymer as an
alternative binder can help reduce CO2 emission of concrete. The
binder of geopolymer concrete is different from the ordinary Portland
cement concrete. Geopolymer Concrete specimens were prepared
with different concentration of NaOH solution M10, M14, and, M16
and cured at 60ºC in duration of 24 hours and 8 hours, in addition to
the curing in direct sunlight. Thus, it is necessary to study the effects
of the geopolymer binder on the behavior of concrete. Concrete is
made by using geopolymer technology is environmental friendly and
could be considered as part of the sustainable development. In this
study, the Local Alkaline Activator in Egypt and crashed stone as
coarse aggregate in fly ash based-geopolymer concrete was
investigated. This paper illustrates the development of mechanical
properties. Since the gained compressive strength for geopolymer
concrete at 28 days was in the range of 22.5MPa – 43.9MPa.
Effect of Fly Ash Fineness on Sorption Properties of Geopolymers Based On Liquid Glass
Fly ash (FA) thanks to the significant presence of SiO2
and Al2O3 as the main components is a potential raw material for
geopolymers production. Mechanical activation is a method for
improving FA reactivity and also the porosity of final mixture; those
parameters can be analysed through sorption properties. They have
direct impact on the durability of fly ash based geopolymer mortars.
In the paper, effect of FA fineness on sorption properties of
geopolymers based on sodium silicate, as well as relationship
between fly ash fineness and apparent density, compressive and
flexural strength of geopolymers are presented. The best results in the
evaluated area reached the sample H1, which contents the highest
portion of particle under 20μm (100% of GFA). The interdependence
of individual tested properties was confirmed for geopolymer
mixtures corresponding to those in the cement based mixtures: higher
is portion of fine particles < 20μm, higher is strength, density and
lower are sorption properties. The compressive strength as well as
sorption parameters of the geopolymer can be reasonably controlled
by grinding process and also ensured by the higher share of fine
particle (to 20μm) in total mass of the material.
Study of Fly Ash Geopolymer Based Composites with Polyester Waste Addition
In the present work, fly ash geopolymer based
composites including polyester (PES) waste were studied. Specimens
of three compositions were prepared: (a) fly ash geopolymer with 5%
PES waste; (b) fly ash geopolymer mortar with 5% PES waste; (c) fly
ash geopolymer mortar with 6.25% PES waste. Compressive and
bending strength measurements, water absorption test and
determination of thermal conductivity coefficient were performed.
The results showed that the addition of sand in a mixture of
geopolymer with 5% PES content led to higher compressive strength,
while it increased water absorption and reduced thermal conductivity
coefficient. The increase of PES addition in geopolymer mortars
resulted in a more dense structure, indicated by the increase of
strength and thermal conductivity and the decrease of water
A Study on Bond Strength of Geopolymer Concrete
This paper presents the experimental investigation on
the bond behavior of geo polymer concrete. The bond behavior of
geo polymer concrete cubes of grade M35 reinforced with 16 mm
TMT rod is analyzed. The results indicate that the bond performance
of reinforced geo polymer concrete is good and thus proves its
application for construction.
An Experimental Investigation of Bond Properties of Reinforcements Embedded in Geopolymer Concrete
Geopolymer concretes are new class of construction
materials that have emerged as an alternative to Ordinary Portland
cement concrete. Considerable researches have been carried out on
material development of geopolymer concrete; however, a few studies
have been reported on the structural use of them. This paper presents
the bond behaviors of reinforcement embedded in fly ash based
geopolymer concrete. The development lengths of reinforcement for
various compressive strengths of concrete, 20, 30 and 40 MPa, and
reinforcement diameters, 10, 16 and 25 mm, are investigated. Total 27
specimens were manufactured and pull-out test according to EN 10080
was applied to measure bond strength and slips between concrete and
reinforcements. The average bond strengths decreased from 23.06MPa
to 17.26 MPa, as the diameters of reinforcements increased from
10mm to 25mm. The compressive strength levels of geopolymer
concrete showed no significant influence on bond strengths in this
study. Also, the bond-slip relations between geopolymer concrete and
reinforcement are derived using non-linear regression analysis for
various experimental conditions.
High Performance Fibre Reinforced Alkali Activated Slag Concrete
The main objective of the study is focused in
producing slag based geopolymer concrete obtained with the addition
of alkali activator. Test results indicated that the reaction of silicates
in slag is based on the reaction potential of sodium hydroxide and the
formation of alumino-silicates. The study also comprises on the
evaluation of the efficiency of polymer reaction in terms of the
strength gain properties for different geopolymer mixtures.
Geopolymer mixture proportions were designed for different binder
to total aggregate ratio (0.3 & 0.45) and fine to coarse aggregate ratio
(0.4 & 0.8). Geopolymer concrete specimens casted with normal
curing conditions reported a maximum 28 days compressive strength
of 54.75 MPa. The addition of glued steel fibres at 1.0% Vf in
geopolymer concrete showed reasonable improvements on the
compressive strength, split tensile strength and flexural properties of
different geopolymer mixtures. Further, comparative assessment was
made for different geopolymer mixtures and the reinforcing effects of
steel fibres were investigated in different concrete matrix.
A Prospective Study on Alkali Activated Bottom Ash-GGBS Blend in Paver Blocks
This paper presents a study on use of alkali activated bottom ash (BA) and ground granulated blast furnace slag (GGBS) blend in paver blocks. A preliminary effort on alkali-activated bottom ash, blast furnace slag based geopolymer (BA-GGBS-GP) mortar with river sand was carried out to identify the suitable mix for paver block. Several mixes were proposed based on the combination of BA-GGBS. The percentage ratio of BA: GGBS was selected as 100:0, 75:25, 50:50, 25:75 and 0:100 for the source material. Sodium based alkaline activators were used for activation. The molarity of NaOH was considered as 8M. The molar ratio of SiO2 to Na2O was varied from 1 to 4. Two curing mode such as ambient and steam curing 60°C for 24 hours were selected. The properties of paver block such as compressive strength split tensile strength, flexural strength and water absorption were evaluated as per IS15658:2006. Based on the preliminary study on BA-GGBS-GP mortar, the combinations of 25% BA with 75% GGBS mix for M30 and 75% BA with 25% GGBS mix for M35 grade were identified for paver block. Test results shows that the combination of BA-GGBS geopolymer paver blocks attained remarkable compressive strength under steam curing as well as in ambient mode at 3 days. It is noteworthy to know BA-GGBS-GP has promising future in the construction industry.
Stress versus Strain Behavior of Geopolymer Cement under Triaxial Stress Conditions in Saline and Normal Water
Geopolymer cement was evaluated as wellbore sealing material for carbon dioxide geosequestration application. Curing of cement system in saline water and strength testing in triaxial stress state condition under lateral confinement is relevant to primary cementing in CO2 geosequestration wellbore in saline aquifer. Geopolymer cement was cured in saline water (both at ambient conditions for 28 days and heated (60°C) conditions for 12 hours) and tested for triaxial strength at different levels of lateral confinement. Normal water and few other curing techniques were also studied both for geopolymer and API ‘G’ cement. Results reported were compared to evaluate the suitability of saline water for curing of geopolymer cement. Unconfined compression test results showed higher strength for curing in saline water than normal water. Besides, testing strength under lateral confinement demonstrated the material failure behavior from brittle to plastic.
Flowability and Strength Development Characteristics of Bottom Ash Based Geopolymer
Despite of the preponderant role played by cement among the construction materials, it is today considered as a material destructing the environment due to the large quantities of carbon dioxide exhausted during its manufacture. Besides, global warming is now recognized worldwide as the new threat to the humankind against which advanced countries are investigating measures to reduce the current amount of exhausted gases to the half by 2050. Accordingly, efforts to reduce green gases are exerted in all industrial fields. Especially, the cement industry strives to reduce the consumption of cement through the development of alkali-activated geopolymer mortars using industrial byproducts like bottom ash. This study intends to gather basic data on the flowability and strength development characteristics of alkali-activated geopolymer mortar by examining its FT-IT features with respect to the effects and strength of the alkali-activator in order to develop bottom ash-based alkali-activated geopolymer mortar. The results show that the 35:65 mass ratio of sodium hydroxide to sodium silicate is appropriate and that a molarity of 9M for sodium hydroxide is advantageous. The ratio of the alkali-activators to bottom ash is seen to have poor effect on the strength. Moreover, the FT-IR analysis reveals that larger improvement of the strength shifts the peak from 1060 cm–1 (T-O, T=Si or Al) toward shorter wavenumber.
Effect of Incorporating Silica Fume in Fly Ash Geopolymers
This paper presents results of an experimental study performed to investigate effect of incorporating silica fume on physico-mechanical properties and durability of resulting fly ash geopolymers. Geopolymer specimens were prepared by activating fly ash incorporated with additional silica fume in the range of 2.5% to 5%, with a mixture of sodium hydroxide and sodium silicate solution having Na2O content of 8%. For studying durability, 10% magnesium sulphate solution was used to immerse the specimens up to a period of 15 weeks during which visual observation, weight changes and strength changes were monitored regularly. Addition of silica fume lowers performance of geopolymer pastes. However, in mortars, addition of silica fume significantly enhanced physico-mechanical properties and durability.
Effect of Curing Conditions on Strength of Fly ash-based Self-Compacting Geopolymer Concrete
This paper reports the results of an experimental work
conducted to investigate the effect of curing conditions on the
compressive strength of self-compacting geopolymer concrete
prepared by using fly ash as base material and combination of sodium
hydroxide and sodium silicate as alkaline activator. The experiments
were conducted by varying the curing time and curing temperature in
the range of 24-96 hours and 60-90°C respectively. The essential
workability properties of freshly prepared Self-compacting
Geopolymer concrete such as filling ability, passing ability and
segregation resistance were evaluated by using Slump flow,
V-funnel, L-box and J-ring test methods. The fundamental
requirements of high flowability and resistance to segregation as
specified by guidelines on Self-compacting Concrete by EFNARC
were satisfied. Test results indicate that longer curing time and curing
the concrete specimens at higher temperatures result in higher
compressive strength. There was increase in compressive strength
with the increase in curing time; however increase in compressive
strength after 48 hours was not significant. Concrete specimens cured
at 70°C produced the highest compressive strength as compared to
specimens cured at 60°C, 80°C and 90°C.
Effect of Superplasticizer and NaOH Molarity on Workability, Compressive Strength and Microstructure Properties of Self-Compacting Geopolymer Concrete
The research investigates the effects of super plasticizer and molarity of sodium hydroxide alkaline solution on the workability, microstructure and compressive strength of self compacting geopolymer concrete (SCGC). SCGC is an improved way of concreting execution that does not require compaction and is made by complete elimination of ordinary Portland cement content. The parameters studied were superplasticizer (SP) dosage and molarity of NaOH solution. SCGC were synthesized from low calcium fly ash, activated by combinations of sodium hydroxide and sodium silicate solutions, and by incorporation of superplasticizer for self compactability. The workability properties such as filling ability, passing ability and resistance to segregation were assessed using slump flow, T-50, V-funnel, L-Box and J-ring test methods. It was found that the essential workability requirements for self compactability according to EFNARC were satisfied. Results showed that the workability and compressive strength improved with the increase in superplasticizer dosage. An increase in strength and a decrease in workability of these concrete samples were observed with the increase in molarity of NaOH solution from 8M to 14M. Improvement of interfacial transition zone (ITZ) and micro structure with the increase of SP and increase of concentration from 8M to 12M were also identified.
Compressive Strength and Workability Characteristics of Low-Calcium Fly ash-based Self-Compacting Geopolymer Concrete
Due to growing environmental concerns of the cement
industry, alternative cement technologies have become an area of
increasing interest. It is now believed that new binders are
indispensable for enhanced environmental and durability
performance. Self-compacting Geopolymer concrete is an innovative
method and improved way of concreting operation that does not
require vibration for placing it and is produced by complete
elimination of ordinary Portland cement.
This paper documents the assessment of the compressive strength
and workability characteristics of low-calcium fly ash based selfcompacting
geopolymer concrete. The essential workability
properties of the freshly prepared Self-compacting Geopolymer
concrete such as filling ability, passing ability and segregation
resistance were evaluated by using Slump flow, V-funnel, L-box and
J-ring test methods. The fundamental requirements of high
flowability and segregation resistance as specified by guidelines on
Self Compacting Concrete by EFNARC were satisfied. In addition,
compressive strength was determined and the test results are included
here. This paper also reports the effect of extra water, curing time and
curing temperature on the compressive strength of self-compacting
geopolymer concrete. The test results show that extra water in the
concrete mix plays a significant role. Also, longer curing time and
curing the concrete specimens at higher temperatures will result in
higher compressive strength.
Effect of Na2O Content on Performance of Fly ash Geopolymers at Elevated Temperature
The present paper reports results of an experimental
program conducted to study performance of fly ash based
geopolymer pastes at elevated temperature. Three series of
geopolymer pastes differing in Na2O content (8.5%, 10% and 11.5%)
were manufactured by activating low calcium fly ash with a mixture
of sodium hydroxide and sodium silicate solution. The paste
specimens were subjected to temperatures as high as 900oC and the
behaviour at elevated temperatures were investigated on the basis of
physical appearance, weight losses, residual strength, shrinkage
measurements and sorptivity tests at different temperatures. Scanning
electron microscopy along with EDX and XRD tests were also
conducted to examine microstructure and mineralogical changes
during the thermal exposure. Specimens which were initially grey
turned reddish accompanied by appearance of small cracks as the
temperature increased to 900oC. Loss of weight was more in
specimens manufactured with highest Na2O content. Geopolymer
paste specimen containing minimum Na2O performed better than
those with higher Na2O content in terms of residual compressive
Compressive Strength and Interfacial Transition Zone Characteristic of Geopolymer Concrete with Different Cast In-Situ Curing Conditions
The compressive strength development through
polymerization process of alkaline solution and fly ash blended with Microwave Incinerated Rice Husk Ash (MIRHA) is described in this
paper. Three curing conditions, which are hot gunny curing, ambient
curing, and external humidity curing are investigated to obtain the suitable curing condition for cast in situ provision. Fly ash was
blended with MIRHA at 3%, 5%, and 7% to identify the effect of blended mixes to the compressive strength and microstructure
properties of geopolymer concrete. Compressive strength results
indicated an improvement in the strength development with external humidity curing concrete samples compared to hot gunny curing and
ambient curing. Blended mixes also presented better performance
than control mixes. Improvement of interfacial transition zone (ITZ)
and micro structure in external humidity concrete samples were also
identified compared to hot gunny and ambient curing.
Effect of Na2O Content on Durability of Geopolymer Mortars in Sulphuric Acid
This paper presents the findings of an
experimental investigation to study the effect of alkali content
in geopolymer mortar specimens exposed to sulphuric acid.
Geopolymer mortar specimens were manufactured from Class F fly
ash by activation with a mixture of sodium hydroxide and sodium
silicate solution containing 5% to 8% Na2O. Durability of specimens
were assessed by immersing them in 10% sulphuric acid solution and
periodically monitoring surface deterioration and depth of
dealkalization, changes in weight and residual compressive strength
over a period of 24 weeks. Microstructural changes in the specimens
were studied with Scanning electron microscopy (SEM) and EDAX.
Alkali content in the activator solution significantly affects the
durability of fly ash based geopolymer mortars in sulphuric acid.
Specimens manufactured with higher alkali content performed better
than those manufactured with lower alkali content. After 24 weeks in
sulphuric acid, specimen with 8% alkali still recorded a residual
strength as high as 55%.