Sep 30, 2021, 17:10 PM by Trevor Hileman

Part 1: Overview of Binders in Refractory Concretes
Part 2: QuikTurn Vs. Rescobond Vs. EZ Est
Part 3: Laboratory Results of QuikTurn Vs. Rescobond Vs. EZ EST

In order to evaluate the relative advantages of each refractory type, samples of 60% alumina castables were batched in the laboratory, mixed with water and allowed to set. Initially physical properties for bulk density, compressive strength and abrasion resistance were determined. Table 1 (below) lists common physical properties for samples of the three types of refractory concretes using standard ASTM methods. Bulk density (pounds per cubic foot, pcf) is measured after heating to 1500°F (816°C). Compressive strength, also called cold crushing strength (CCS), was measured in the green state after 24 hour cure at room temperature, after drying to 220°F (104°C), after heating to 600°F (316°C) and after heating to 1500°F.

Refractory	Binder	Density	CCS	CCS	CCS	CCS
		after heating to 1500ºF (pcf)	Green (undried) (psi)	after drying to 220ºF (psi)	after heating to 600ºF (psi)	after heating to 1500ºF (psi)
QuikTurn 60PC	Cement	152	4.390	9,060	8,560	12,200
Rescobond 3000	Chemical	150	3,250	8,660	10,190	9,800
EZ Est 60 PC	C/S	155	1,420	4,720	4,820	6,460

Table 1. Physical properties of 60% alumina castables using the three binders

The cement-bonded refractory, QUIKTURN 60 PC, exhibited the highest strengths in all tests. QUIKTURN 60 PC’s strength more than doubled after drying. After heating to 600°F (316°C), the QUIKTURN 60 PC sample showed a small loss in strength, likely due to the dehydration of some of the cement phases, but increased in strength after heating to 1500°F (816°C).

The phosphate-bonded casting mix, RESCOBOND 3000, developed good strength in the green state, and like the cement- bonded material, more than doubled in strength after drying. On further heating to 600°F (316°C), strength showed additional improvement. RESCOBOND 3000 had essentially the same strength after heat treatment at 1500°F (816°C) as after heating to 600°F (316°C). These data are consistent with the phosphate bond essentially being formed complete by 600°F.

Abrasion resistance is indicative of a refractory concrete’s resistance to a scraping or scratching medium. Abrasion loss is measured at room temperature using the ASTM C-704 procedure typically after heating the sample to 1500°F (816°C). In the ASTM C-704 test, 1,000 grams silicon carbide grit abrades the sample at room temperature and the volume lost (in cc’s) is reported. A low number (less volume abraded) indicates better abrasion resistance.

Abrasion resistance was tested on the three refractory types in the green state after curing, after drying to 220°F (104°C), after drying and heating to 600°F (316°C), and after drying and heating to 1500°F (816°C). Abrasion resistance trended with cold crushing strength (CCS).

Refractory	Binder	ASTM C-704	ASTM C-704	ASTM C-704	ASTM C-704
		Abrasion cc, loss after drying to 220ºF	Abrasion cc, loss after drying to 600ºF	Abrasion cc, loss after drying to 1500ºF	Abrasion cc, loss after drying to 2200ºF
QuikTurn 60 PC	Cement	6.7	9.2	5.3	5.2
Rescobond 3000	Chemical	12.2	9.9	6.1	8.8
EZ Est 60 PC	C/S	22.3	20.6	9.1	5.6

In addition to physical property tests, other application-related tests were conducted to evaluate the suitability of each refractory type in various types of service.

Alkali resistance is a topic of interest to cement plant operators. Many vessels in the lower preheater and frequently in the cooler have linings that can be susceptible to reaction with alkali, primarily potash (K2O). Alkali reactions with alumino- silicate refractories are expansive in nature, as the products of reaction with alkali are significantly larger in volume than the original refractory. The expansion can cause disruption of the refractory bonding matrix and lead to cracking and spalling.

One such test used by the refractory industry to evaluate alkali resistance is a simple cup test. In this test, a refractory sample is made that contains a 40-mm diameter, 40 mm deep hole. The sample is dried at 230°F (110°C) and fired in a kiln to 2192°F (1200°C) for five hours. Potassium carbonate (K2CO3) is packed into the hole of the refractory cup. A refractory lid is cemented into place over the filled cup. The cup is then fired to 2012°F (1100°C) for five hours and then cooled. The specimen is cut into halves and visually examined. Cracks indicate alkali reactions and give the sample an unsatisfactory rating. The samples must also have a penetration no greater than 3-mm in order to receive a satisfactory rating.

QUIKTURN 60 PC (left) and RESCOBOND 3000 (center) refractories show good alkali resistance with no cracking. Colloidal silica-bonded EZ EST 60 PC (right) also exhibits strong alkali resistance.

In appearance, all three refractory types had equivalent alkali resistance, with none of the sample cups exhibiting cracking, and all three received a satisfactory rating.

Refractory	Binder	Alkali Cup Test
		Cracking	Penetration	Rating
QuikTurn 60PC	Cement	No	< 1	Sat
Rescobond 3000	Chemical	No	< 1	Sat
EZ Est 60 PC	C/S	No	0	Sat

Alkali cup test results for the three refractory types

Another property of interest is the adherence of the refractory material to an existing refractory substrate. Measuring adherence to an existing refractory is difficult and can be variable. A non-standard test has been devised to measure this property based on the Modulus of Rupture (MOR) test for flexural strength. MOR bars of a conventional castable refractory are cast and dried. The bars are broken in typical MOR fashion, and a broken half bar is re-inserted into the MOR bar molds. The candidate refractory is then cast into the remaining portion of the bar mold cavity of the bar. The candidate refractory is allowed to set, and the jointed bar is then removed from the mold and fired to 1500°F (816°C). After cooling, the jointed bar is again broken in the MOR fashion. The MOR pressure is then recorded as the adherence strength.

As expected, the RESCOBOND 3000 jointed bar had the highest adherence strength, closely followed by the silica-bonded concrete sample (SBC). The QUIKTURN 60 PC had the lowest adherence and after heating to 2200°F (1204°C), there was no adherence at all to the original broken refractory piece.

Also as expected, the adherence strength of the silica-bonded refractory, EZ EST 60 PC, increased as the heat treatment temperature increased, consistent with the compressive strength characteristics of this material.

Refractory	Binder	Adherence Test	Adherence Test	Adherence Test
		after heating to 220ºF (psi)	after heating to 600ºF (psi)	after heating to 2200ºF (psi)
Quikturn 60 PC	Cement	249	134	0
Rescobond 3000	Chemical	419	130	800
EZ Est 60 PC	C/S	73	286	610