Potential of acidic volcanic rocks from the Serra Geral group as a partial replacement for Portland cement

Meinhart, Alice Helena; Borges, Cleyton Machado; Maus, Kim Lisboa Daut; Polesello, Eduardo; Sander, Andrea; Koppe, Angélica; Arnold, Daiana Cristina Metz

doi:10.1590/s1678-86212026000100991

Special issue: the best papers of SBCC 2025 • Ambiente Construído 26 • Jan-Dec 2026 • https://doi.org/10.1590/s1678-86212026000100991 linkcopy

Potential of acidic volcanic rocks from the Serra Geral group as a partial replacement for Portland cement

Potencial pozolânico de rochas vulcânicas ácidas do grupo Serra Geral como substituição parcial ao cimento Portland

Authorship SCIMAGO INSTITUTIONS RANKINGS

Searching for natural elements whose processing does not require burning and/or decarbonation, this research aimed to test acidic volcanic rocks from the Serra Geral Group as a partial substitute for Portland cement. After selecting relevant areas from consolidated bibliographies, rocks were selected in Caxias do Sul, Cambará do Sul, and São Joaquim in southern Brazil. Petrography confirmed the presence of volcanic glass in all samples. Pozzolanic activity was analyzed using standardized tests, including lime fixation, electrical conductivity variation, and amorphous material content. Both met the standardized chemical requirements but showed limited performance in pozzolanic activity with lime over 7 days. In physical tests, only Caxias do Sul and São Joaquim achieved the minimum required compressive strength. Caxias do Sul stood out for containing 52% amorphous material and having the highest consumption of Ca(OH)₂. Evaluating electrical conductivity, Caxias do Sul and Cambará do Sul showed variable pozzolanicity, while São Joaquim was considered non-pozzolanic. In summary, the rocks demonstrated pozzolanic properties, validating the use as supplementary cementitious materials. Therefore, this study contributes to the development of eco-efficient binders that are in line with the principles of the modern circular economy.

Keywords
Volcanic rocks; Pozzolanicity; Supplementary cementitious materials

Parameter	Result	Parameter	Result
SiO₂	18.42	Hot expansion (mm)	0.05
Al₂O₃	4.39	Initial setting time (min)	154
CaO	61.70	Final setting time (min)	206
MgO	3.23	Normal consistency (%)	28.7
SO₃	2.74	Blaine Fineness (cm²/g)	4269
Fe₂O₃	2.94	Compressive Strength – 1 day (MPa)	26.3
Loss on ignition	3.59	Compressive Strength – 3 days (MPa)	38.4
Free CaO	1.75	Compressive Strength – 7 days (MPa)	44.5
Insoluble residue	0.77	Compressive Strength – 28 days (MPa)	52.5

Sample	Numerical Indicators (%)
Sample	GOF	Rp	Rwp	Rexp
Caxias do Sul	4.87	9.33	13.12	2.69
Cambará do Sul	4.88	10.04	13.79	2.8
São Joaquim	4.41	8.73	12.42	2.81

Material	Reference Mortar	Mortar with replacement
Portland cement (g)	624 ± 0.4	468 ± 0.4
Material to be tested (g)	-	156 ± 0.2
Fine aggregate (g)	1872	1872
Water (g)	300 ± 0.2	300 ± 0.2

Physical characterization	Caxias do Sul	Cambará do Sul	São Joaquim
Specific mass (g/cm³)	2.54	2.60	2.58
Particle size (D10) (µm)	2.82	2.64	3.09
Particle size (D50) (µm)	12.14	12.26	14.93
Particle size (D90) (µm)	29.14	37.01	41.05
Average particle size (µm)	14.96	17.23	19.71
Chemical characterization	Caxias do Sul	Cambará do Sul	São Joaquim
MgO (%)	1.01	0.56	0.59
Al₂O₃ (%)	13.98	13.59	13.26
SiO₂ (%)	64.95	64.31	62.71
Fe₂O₃ (%)	7.58	6.67	6.29
P₂O₅ (%)	0.61	0.61	0.58
SO₃ (%)	0	0	0
Cl (%)	0.17	0.16	0.17
K₂O (%)	2.53	3.71	3.38
CaO (%)	4.61	4.61	4.61
TiO₂ (%)	1.10	1.01	0.97
V₂O₅ (%)	0.02	0.01	0.02
Cr₂O₃ (%)	< 0.01	< 0.01	< 0.01
MnO (%)	0.14	0.14	0.14
CuO (%)	0.01	0.01	0.02
ZnO (%)	0.01	0.01	0.01
Ga₂O₃ (%)	< 0.01	< 0.01	0.01
Rb₂O (%)	0.02	0.02	0.02
SrO (%)	0.02	0.02	0.02
Y₂O₃ (%)	< 0.01	< 0.01	< 0.01
ZrO₂ (%)	0.04	0.04	0.04
Nb₂O₅ (%)	< 0.01	< 0.01	< 0.01
BaO (%)	0.03	0.04	0.038
Eu₂O₃ (%)	0.04	0.04	0.04
Yb₂O₃ (%)	< 0,01	< 0.01	< 0.01
PbO (%)	< 0.01	< 0.01	< 0.01
ThO₂ (%)	< 0.01	< 0.01	< 0.01
LOI (%)	3.06	4.38	7.04
SiO₂ + AlO₃ (%)	78.93	77.90	75.97
SiO₂ + AlO₃ + FeO (%)	86.52	84.58	82.26
Total (%)	100	99.99	100

Properties	Reference values for Class “N”	Results			Compliance with requirements and respective reference values
Properties	Reference values for Class “N”	Caxias do Sul	Cambará do Sul	São Joaquim
SiO₂ + AlO₃ + FeO	≥ 70%	86.52%	84.57%	82.26%	All samples meet the requirement
SO₃	≤ 4%	Not Detected	Not Detected	Not Detected	All samples meet the requirement
Moisture content	≤ 3%	0.5%	0.9%	0.5%	All samples meet the requirement
Loss on ignition	≤ 10%	3.06%	4.38%	7.04%	All samples meet the requirement

Properties	Reference values for Class “N”	Results			Compliance with requirements and respective reference values
Properties	Reference values for Class “N”	Caxias do Sul	Cambará do Sul	São Joaquim
Material retained on the 45 µm sieve (maximum %)	< 20%	0%	0%	0%	All samples meet the requirement
IAP - Pozzolanic activity index with lime at 7 days (MPa)	≥ 6 MPa	0.38 MPa	0.34 MPa	0.22 MPa	None of the samples meet the requirement

Sample	Reference values for Class “N”	Strength activity index at 28 days	Compliance with requirements
Caxias do Sul	≥ 90%	94.08%	Meets the requirement
Cambará do Sul	≥ 90%	80.22%	Does not meet the requirement
São Joaquim	≥ 90%	92.9%	Meets the requirement

Sample	Determination of the fixed calcium hydroxide content – Modified Chapelle method	Luxán, Madruga and Saavedra (1989) method
Sample		Conductivity (µS/cm)	Classification according to Luxán et al. (1989)
Caxias do Sul	539.62 mg Ca(OH)₂/g	0.49 µS/cm	Variable pozzolanicity
Cambará do Sul	358.51 mg Ca(OH)₂/g	0.70 µS/cm	Variable pozzolanicity
São Joaquim	299.38 mg Ca(OH)₂/g	0.28 µS/cm	Non-pozzolanic

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[1] Source: adapted from the supplier (2022).