PRACTICAL APPLICATION OF THE MICROWAVE OVEN IN THE GEOTECHNICAL LABORATORY

JASTRZĘBSKA, Małgorzata

doi:10.21307/acee-2019-026

Figures & Tables

Curves of grain size of non-cohesive soils, black line – FSa, gray line – saGr

Difference between results of moisture contents from microwave oven and conventional oven for FSa, siCl and saGr specimens (variant 1)

Change of specimens moisture content during drying in a conventional oven (variant 1) for FSa, siCl and saGr

Change of specimens moisture content during drying in a microwave oven (variants 1 and 2) for FSa, siCl and saGr

Change of specimens drying time in a microwave oven depending on their initial moisture for FSa, siCl and saGr (variant 1)

Change of specimens drying time in a microwave oven and conventional oven depending on their initial mass for FSa, siCl and saGr (variant 2)

Change of specimens drying time in a microwave oven depending on their number for FSa and siCl (variant 3)

Research program (w – specimen moisture; m – specimen mass; n – specimen number in one drying cycle)

Type of soil	Parameter	Variant 1		Variant 2		Variant 3
Type of soil	Parameter	(MO-A)(MO-B)	(CO)	(MO-A)	(CO)	(MO-A)
FSa(SP)	w	3% ÷ 43% every 4%43% ÷ 103% every 5%		45%	45%	45%
	m	25 g	25 g	25 g, 50 g, 75 g,100 g, 125 g, 300 g		25 g
	n	1	-	1	-	1, 2, 3, 5
SaGr (GW)	w	3% ÷ 43%every 4%43% ÷ 103%every 5%	3% ÷ 43%every 4 %43% ÷ 48%every 5%	45%	45%	-
	m	300 g	300 g	300 g	300 g	-
	n	1	-	1	-	-
SiCl (CH)	w	3% ÷ 43% every 4%43% ÷ 103% every 5%		45%	45%	45%
	m	25 g	25 g	25 g, 50 g, 75 g,100 g, 125 g		25 g
	n	1	-	1	-	1, 2, 3, 5

Summary of selected measurements of moisture and drying time for FSa, siCl and saGr conducted in conventional oven for variant 1

Conventional oven (CO) – variant 1
m = 25 g			m = 300 g
Meas. time	FSa	siCl	Meas. time	saGr
t	w _avg	w _avg	t	w _avg
(min)	(%)	(%)	(min)	(%)
0	2.83	3.26	0	3.02
20	0.27	1.82	20	2.16
40	0.08	0.92	40	1.52
60	0.02	0.45	60	0.84
80	0.02	0.25	80	0.40
110	0.02	0.12	110	0.08
140	0.02	0.12	140	0.03
170	0.02	0.12	170	0.01
200	0.02	0.08	200	0.01
230	0.02	0.02	230	0.01
1440	0.00	0.00	1440	0.00
0	23.10	23.37	0	22.80
60	1.01	2.15	60	16.01
230	0.03	0.17	230	1.44
1440	0.00	0.00	1440	0.00
0	42.65	42.78	0	34.68
60	19.20	20.76	60	26.74
230	0.00	0.26	230	5.90
1440	0.00	0.00	260	3.56
0	63.16	63.55	290	1.71
60	38.38	30.05	1440	0.00
230	0.00	0.13	0	42.96
1440	0.00	0.00	60	32.66
0	83.20	83.18	230	7.02
60	30.19	43.00	260	4.15
230	0.00	0.00	290	2.20
1440	0.00	0.00	1440	0.00
0	102.98	103.11	0	48.05
20	82.60	88.30	20	45.99
40	59.65	71.54	40	43.00
60	41.06	50.51	60	40.09
80	20.68	29.68	80	36.76
110	0.49	5.09	110	32.20
140	0.08	0.20	140	26.65
170	0.00	0.04	170	22.34
200	0.00	0.04	200	17.22
230	0.00	0.04	230	10.68
1440	0.00	0.00	260	7.65
-	-	-	290	4.03
-	-	-	1440	0.00

Summary of moisture measurements and drying time for FSa, siCl and saGr conducted in microwave oven for variant 1

Microwave oven (MO-A+MO-B) – variant 1
m = 25 g				m = 300 g
FSa		siCl		saGr
wavg	tavg	wavg	tavg	wavg	tavg
(%)	(min)	(%)	(min)	(%)	(min)
2.83	2.8	3.10	1.8	2.97	5.5
6.66	4.3	7.41	2.3	7.20	7
10.70	4	11.38	2.8	11.28	7
14.93	4.5	15.28	3.5	15.21	8
18.90	3.8	19.07	4	19.01	8
22.88	3.8	23.04	4	23.20	9
26.94*	11.5	27.10	4	27.09	9
30.46	10.5	31.09	4	31.18	9.5
35.43	11	35.15	4	35.03	10.5
38.57	11.5	39.01	4	39.18	10.5
42.92	11	42.64	4	42.93	11
48.30	11	48.19	4.5	48.04	11
52.95	10.5	53.03	4.5	53.37	12
58.19	11	58.27	4.5	57.84	13
63.05	10	62.72	4.5	63.10	13
67.83	11.5	67.74	4.5	68.13	14
73.47	9.5	73.18	5	72.81	14
78.11	11	77.97	5	77.99	14
82.84	11	82.39	5	82.79	14.5
87.88	10.5	87.63	5	87.81	15
92.90	11	92.81	5	92.99	15
98.15	12.5	98.22	5	98.10	15.5
103.20	12	103.09	5	102.83	16
45.12	12	45.01	4	44.95	11

Summary of details, results and recommendations for determining the moisture content of soils in the microwave oven based on previous and own researches

References	Output power of microwave [W]	Type of soil	Mass of specimen [g]	Drying time [min]		Remarks and recommendations
1	2	3	4	5 (min)	6 (max)	7
Ryley (1969)	500-2000	Sand, limestone gravel, clays, organic earth, chalk, coal	100	10	15	1. Large errors in the case of clay mixed with gypsum.2. Ignition of coal in the microwave oven.
Routledge & Sabey (1976)	-	Loamy sand, clay (with different initial moisture)	5, 10 and 25	5	35	1. The increase in moisture content and the number of specimens in the cycle increases the duration of the test.
Hagerty et al. (1990a, 1990b)	700	Sand, silt, clay, tile clay, peat clay, bentonite, loess, aggregate	50, 100 and 200	8	105	1. Test in cycles: 1 min (2 min) heating, then 1 min cooling and weighing the specimen.
Gilbert (1988, 1991)	-	Clays, organic clays, silts, sands, gravels, fly ash (depending on the soil w ₀ = 2%–495%)	20–1280	3’38’’	30’7’’	1. Automated microwave oven drying.2. Safety instructions.3. The possibility of exploding soils and rocks.4. Recommended specimen mass 80 g (100 g) – 200 g.5. Mixing the soil during drying may cause its loss, which affects the erroneous determination of moisture.
Gaspard (2002)	650	Clay, silt, sand (depending on the soil w ₀ = 27%–45%)	500	11,2 (SMWO) 19,5 (CMWO)	31,7 (SMWO) 52,7 (CMWO)	1. Due to costs, the recommendation for SMWO (Standard Microwave Oven) method, not for CMWO (Computer Controlled Microwave Oven).
Gołębiewska et al. (2003)	800	Loamy sand, silt, clay, clay loam, medium sand	I _p=0-10%: 20, 50, 100 I _p=10-30%, I _p >30%: 10, 30, 60	3	10	1. Control measurement every 1 min in the range from 1–10 min.2. Dry 3 specimens at the same time.
Chung & Ho (2008)	700-1700	Silt loam	100–1000	8,5	50	1. Initial drying for 3 min, for the first minute taking measurement every 10 seconds.
Suwandi et al. (2009)	700	Clay (depending on the soil w ₀ = 67% –174%)	100–1000	14,7	22	1. Testing procedure based on ASTM D4643-00.
Daod (2012)	900	Clay, silty clay	150–200	-	-	1. Recommended mass specimen for determination liquidity limit 50-60 g.2. Measurement in the interval every 10 min.
Grymowicz & Jastrzębska (2015)	800	Fine sand, silt, clay	12,531,51816	2	40	1. Moisture content of all specimens increased by 25% in relation to the initial state.2. Drying of 5 specimens at the same time.
Kramarenko et al. (2015, 2016)	900	Clay, clay loam, clay sand, low peat clay (w ₀ = 14%–58%) peat (w ₀ = 2513%)	9–1005–200	5	17	1.1. Recommended drying time:• 30–40 min for peat mass more than 100 g,• 10–15 min for peat mass 30–50 g,• 3–5 min for peat mass 5–10 g.2. Recommended the intervals between control weighing:• about 3–5 min for peat mass more than 50 g,• 1-2 min for peat mass more than 5-10 g and for low peaty soil.3. According to ASTM D 4643 – 00 they suggest the mixing of soil at control weighing.
Cormick (2015)	-	Fine-grained coarse-grained	10–250300–1000	-	-	1. Recommended specimen mass of 150 g.2. Continuous drying for the first 3 min and then every 1 min with mass measurements after each heating cycle, keeping 1 min cooling period before weighing.3. Do not dry the soils with organic content above 10% and bentonites with moisture content greater than 110%.
Jalilian et al. (2017)	90-180-360-600 and 900	Sieved and unsieved soil specimens with 10cc twice of distilled water	50	5	10	1. Heating cycles of 5 min and 10 min with 1 min cooling before weighing.2. Recommended heating power 600 W.3. Recommended heating time 10 min. min cooling before weighing.
ATT-15/96 Kanada	max. possible	-	min. 250	-	-	1. Dry 1 specimen in a cycle.2. Use the same specimen mass and microwave heating level.3. Measurement from 5 min after starting in the interval every 2 min, to stabilize the mass through the specimen.
ASTM 2000 ASTM 2008 USA	700	Most of the soil types. Caution in the case of the soil types:• soil containing significant amounts of halloysite, mica, montmorillonite, gypsum or other hydrated materials• highly organic soils• soils in which the pore water contains dissolved solids	100–1000 (depending on the grain size)	3	-	1. According to ASTM 2000; initial drying for 3 min and then in cycles every 1 min. Mass measurements after each cycle after 1 min (or no) cooling.2. According to ASTM 2008; heating without a break in accordance with the time determined on the basis of nomograms.3. Mix the soil between drying cycles.4. Do not use specimens smaller than 100 g due to the possibility of overheating.
Jastrzębska	800	Fine sand, silty clay, sandy gravel (specimens with different moisture w ₀ = 3%–103%)	25–300	2	17	1. Measurement up to 5 min in the intervals every 30 seconds, then every 1 min to stabilize the mass through the specimen.2. The need to cover specimens due to the possibility of exploding.

Cohesive soil – basic parameters

Parameter	Value siCl (CH)
Specific density, ρ _s (g/cm³)	2.77
Dry density of solid particles, ρ _ds (g/cm³)	1.75
Plastic limit, w _p (%)	25
Liquid limit – cone penetrometer method, w _L (%)	65
Liquid limit - Casagrande method, w _L (%)	75
Optimal moisture, w _opt (%)	18
Swelling pressure, σ _sp (kPa)	97
Free-swell, FS (%)	31.50

Non-cohesive soils – basic parameters Table 2_

Characteristic diameter / Parameter	Value
Characteristic diameter / Parameter	FSa (SP)	saGr (GW)
D ₁₀ (mm)	0.10	0.40
D ₃₀ (mm)	0.20	2.20
D ₅₀ (mm)	0.25	4.50
D ₆₀ (mm)	0.30	5.80
D ₉₀ (mm)	0.70	9.50
Coefficient of curvature, C _c	1.44	2.30
Coefficient of uniformity, C _u	2.50	15.70
Specific density, ρ_s (g/cm³)	2.65	2.65

Summary of moisture measurements and drying time for FSa, siCl and saGr conducted in microwave oven for variant 2

Microwave oven (MO-A) – variant 2 (w ₀ = 45%)
Specimen mass	FSa		siCl		saGr
m	w _avg	t _avg	w _avg	t _avg	w _avg	t _avg
(g)	(%)	(min)	(%)	(min)	(%)	(min)
25	45.12	12	45.01	4	-	-
50	45.23	12	45.41	6	-	-
75	45.61	12	45.01	11	-	-
100	45.39	13.5	45.19	13	-	-
125	45.16	14.5	45.39	16	-	-
300	45.26	17	-	-	44.95	11

Summary of moisture measurements and drying time for FSa and siCl conducted in microwave oven for variant 3

Microwave oven (MO-A) – variant 3
Number of specimens	m ₀ = 25 g, w ₀ = 45%
Number of specimens	FSa		siCl
n	w _avg	t _avg	w _avg	t _avg
(-)	(%)	(min)	(%)	(min)
1	45.12	12	45.01	4
2	44.76	14	44.76	4.75
3	44.72	14.5	44.85	4.75
5	45.04	16.1	44.87	6.8

PRACTICAL APPLICATION OF THE MICROWAVE OVEN IN THE GEOTECHNICAL LABORATORY

Figures & Tables

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Research program (w – specimen moisture; m – specimen mass; n – specimen number in one drying cycle)

Summary of selected measurements of moisture and drying time for FSa, siCl and saGr conducted in conventional oven for variant 1

Summary of moisture measurements and drying time for FSa, siCl and saGr conducted in microwave oven for variant 1

Summary of details, results and recommendations for determining the moisture content of soils in the microwave oven based on previous and own researches

Cohesive soil – basic parameters

Non-cohesive soils – basic parameters Table 2_

Summary of moisture measurements and drying time for FSa, siCl and saGr conducted in microwave oven for variant 2

Summary of moisture measurements and drying time for FSa and siCl conducted in microwave oven for variant 3

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