WITH SourceRecordset AS (
SELECT [index], workcode, value
FROM (
    VALUES(1, 'CL', 5),
    (2, 'CL', 10),
    (3, 'CL', 10),
    (4, 'LI', 10),
    (5, 'LI', 10),
    (6, 'ME', 5),
    (7, 'ME', 5),
    (8, 'CL', 10),
    (9, 'CL', 10),
    (10, 'CL', 5),
    (11, 'ME', 10),
    (12, 'ME', 10)
    ) d([index], workcode, value)
),
Grouped AS (
SELECT [index], workcode, value,
       ROW_NUMBER() OVER(ORDER BY [index])-
       ROW_NUMBER() OVER(PARTITION BY workcode ORDER BY [index]) AS rnDiff
FROM SourceRecordset)
SELECT MIN([index]) AS [index],
       workcode,
       SUM(value) AS value
FROM Grouped
GROUP BY workcode,rnDiff
ORDER BY MIN([index]);

WITH SourceRecordset AS (
SELECT [index], workcode, value
FROM (
    VALUES(1, 'CL', 5),
    (2, 'CL', 10),
    (3, 'CL', 10),
    (4, 'LI', 10),
    (5, 'LI', 10),
    (6, 'ME', 5),
    (7, 'ME', 5),
    (8, 'CL', 10),
    (9, 'CL', 10),
    (10, 'CL', 5),
    (11, 'ME', 10),
    (12, 'ME', 10)
    ) d([index], workcode, value)
)
SELECT [index]=MIN([index]), workcode=MAX(workcode), value=SUM(value)
FROM (
    SELECT [index], workcode, value
        ,rn=[index]-ROW_NUMBER() OVER (PARTITION BY workcode ORDER BY [index])
    FROM SourceRecordset) a
GROUP BY rn
ORDER BY [index]